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The IASLC Lung Cancer Staging Project: Proposals for the Revision of the T Descriptors in the Forthcoming (Seventh) Edition of the TNM Classification for Lung Cancer

      Purpose

      To propose changes in the seventh revision of the tumor, node, metastasis (TNM) classification for lung cancer.

      Methods

      Data on 100,869 patients were submitted to the international database, and data for 18,198 of these patients fulfilled the inclusion criteria for the T component analysis. Survival was calculated for clinical and pathologic T1, T2, T3, T4NOMO completely resected (R0), and for each T descriptor. A running log-rank test was used to assess cutpoints by tumor size. Results were internally and externally validated.

      Results

      On the basis of the optimal cutpoints, pT1NOR0 was divided into pT1a ≤2 cm (n = 1816) and pT1b >2 to 3 cm (n = 1653) with 5-year survival rates of 77 and 71% (p < 0.0001). The pT2NOR0 cutpoints resulted in pT2a >3 to 5 cm (n = 2822), pT2b >5 to 7 cm (n = 825), and pT2c >7 cm (n = 364). Their 5-year survival rates were 58, 49, and 35% (p < 0.0001). For clinically staged N0, 5-year survival was 53% for cT1a, 47% for cT1b, 43% for cT2a, 36% for cT2b, and 26% for cT2c. pT3NO (n = 711) and pT4 (any N) (n = 340) had 5-year survival rates of 38 and 22%. pT4 (additional nodule(s) in the same lobe) (n = 363) had a 5-year survival rate of 28%, similar to pT3 (p = 0.28) and better than other pT4 (p = 0.0029). For pM1 (ipsilateral pulmonary nodules) (n = 180), 5-year survival was 22%, similar to pT4. For cT4-malignant pleural effusion/nodules, 5-year survival was 2%.

      Conclusion

      Recommended changes in the T classification are to subclassify T1 into T1a and T1b, and T2 into T2a and T2b; and to reclassify T2c and additional nodule(s) in the same lobe as T3, nodule(s) in the ipsilateral nonprimary lobe as T4, and malignant pleural or pericardial effusions as M1.

      Key Words

      The sixth edition of the Union Internationale Contre le Cancer (UICC) and the American Joint Committee on Cancer (AJCC) has served as the current tumor, node, metastasis (TNM) staging system for lung cancer since 2002. A new staging project was initiated by the International Association for the Study of Lung Cancer (IASLC) in 1999, with the goal of providing data for the next revision of the international staging system.
      • Goldstraw P
      Report on the international workshop on intrathoracic staging, London, October 1996..
      • Goldstraw P
      The International Staging Committee of the IASLC: its origins and purpose..
      The Cancer Research and Biostatistics office (CRAB) in Seattle, Washington, was selected to develop the database by collecting cases from around the world and to perform statistical analysis of TNM factors in the new dataset. Investigators were invited to share information from their local databases with CRAB. Data on a total of 100,869 patients treated for primary lung cancer from 1990 to 2000 were submitted to CRAB.
      • Goldstraw P
      • Crowley JJ
      The International Association for the Study of Lung Cancer International Staging Project on Lung Cancer..
      Subcommittees were formed from the parent IASLC International Staging Committee, to analyze the new international dataset and to propose appropriate changes for the next revision of the TNM classification for lung cancer. This manuscript provides an analysis of the T descriptors and recommends changes for the next revision of the UICC and AJCC staging system.

      MATERIALS AND METHODS

      Objectives

      To study the prognostic impact of the different descriptors that define the T component of the TNM classification in patients with N0M0 tumors, and to see whether they are useful in classifying non-small cell lung cancer (NSCLC), the T descriptors subcommittee established the following issues as priorities:
      • Clinical and pathologic tumor size in T1 and T2 tumors, excluding other T2 descriptors.
      • Clinical and pathologic T2 descriptors, in general and stratified by tumor size: atelectasis/pneumonitis of less than the whole lung, visceral pleural involvement, and endobronchial location.
      • Clinical and pathologic T3 descriptors: atelectasis/pneumonitis of the whole lung, parietal pleura invasion, chest wall invasion, diaphragmatic invasion, parietal pericardial invasion, mediastinal pleural invasion, endobronchial location, invasion of the phrenic nerve, and Pancoast tumor.
      • Clinical and pathologic T4 descriptors: carinal invasion, invasion of mediastinal tissue, invasion of the great vessels, invasion of the heart, invasion of the recurrent laryngeal nerve, invasion of the esophagus, invasion of the trachea, invasion of the vertebral body, additional nodules in the same lobe as the primary tumor, and malignant pleural and pericardial effusion.
      • Stratification of results by cell type.
      • Stratification of results by completeness of resection.

      Population

      The total number of patients submitted to CRAB was 100,869,
      • Goldstraw P
      • Crowley JJ
      The International Association for the Study of Lung Cancer International Staging Project on Lung Cancer..
      of whom 18,018 patients met the T descriptors subcommittee's initial analytic requirements of M0 NSCLC, a complete set of either cTNM or pTNM, and sufficient T descriptor details to support the assigned T stage (Table 1). On the basis of recommendations by the M descriptors subcommittee, 180 patients with tumors staged as M1 because of additional nodules in an ipsilateral different lobe from the primary tumor were added to the T component analysis, bringing the total analyzed to 18,198. These 18,198 patients originated from four geographical areas, including Europe, North America, Asia, and Australia, and from a variety of data sources (see Table 2).
      TABLE 1Number of M0 Non-small Cell Lung Cancer Cases Passing Initial Screening
      N0Any N
      TotalT1T2T3T4TotalT1T2T3T4
      Clinically staged
       Total19,435633186782484194238,162806616,79463376965
       No. analyzed
      Criteria for T factor analysis: cases must have had at least one T descriptor supporting the assigned T stage and no T descriptors suggesting a higher T stage.
      38968732234486303576010663111677906
      Clinically staged, surgically managed
       Total15,34757707317167858222,438669811,34130491350
       No. analyzed
      Criteria for T factor analysis: cases must have had at least one T descriptor supporting the assigned T stage and no T descriptors suggesting a higher T stage.
      3554828216045611042919262642554169
      Clinically staged, nonsurgically managed
       Total40885611361806136015,7241368545332885615
       No. analyzed
      Criteria for T factor analysis: cases must have had at least one T descriptor supporting the assigned T stage and no T descriptors suggesting a higher T stage.
      3424574301931469140469123737
      Pathologically staged (surgically managed)
       Total15,42850118157165460626,177673814,51433611564
       No. analyzed
      Criteria for T factor analysis: cases must have had at least one T descriptor supporting the assigned T stage and no T descriptors suggesting a higher T stage.
      97243855479771136115,234499580671224948
      # Criteria for T factor analysis: cases must have had at least one T descriptor supporting the assigned T stage and no T descriptors suggesting a higher T stage.
      TABLE 2Number of Non-small Cell Lung Cancer Cases Analyzed by Type of Database, Continent, and Type of Staging (Clinical vs. Pathological)
      Clinically StagedPathologically Staged
      TotalTotalcT1–cT4
      M1 attributable to additional nodules on the same side but on a different lobe from the primary tumor.
      cM1
      TotalpT1–pT4
      M1 attributable to additional nodules on the same side but on a different lobe from the primary tumor.
      pM1
      Total with sufficient T descriptors18,198578457602415,41415,234180
      Clinical trial
       Australia5858580000
       Europe6767670000
       North America15521140114004464460
      Consortium/surgical series
       Asia630700063076183124
       Australia191451510186918690
       Europe41223121311833447340443
       North America789434307797781
      Registry/series
       Asia4654143942027826612
       Australia1231231221000
       Europe22164534530177717770
       North America58531431405115110
      * M1 attributable to additional nodules on the same side but on a different lobe from the primary tumor.
      The NSCLC M0 population with complete cTN included 38,162 patients (Table 1). There was sufficient clinical T descriptor information for 5760 patients, including 339 treated preoperatively, distributed as follows: 68% cN0, 5% cN1, 21% cN2, 4% cN3, and 3% cT4Nx. As for the analysis of the pathologic T, the population excluded neoadjuvant treatment and consisted of 26,177 M0 patients with complete pTN (substitutions of cM for pM were permitted). In 15,234 of these patients, the tumors had sufficient pT descriptors and were distributed as follows: 64% pN0, 19% pN1, 17% pN2, 0.5% pN3, and 0.3% pT4Nx. Table 3 summarizes the distribution of histologic types according to clinical and pathologic T factors. Complete resection (R0) was achieved in 85% of tumors with any pN, and this rate increased to 89% in those with no nodal involvement (pN0) (Table 4).
      TABLE 3Clinical and Pathologic T Stage by Histologic Type
      Clinical TPathologic T
      TotalcT1cT2cT3cT4cM1
      M1 attributable to additional nodules on the same side but on a different lobe from the primary tumor. NOS, not otherwise specified; NSCLC, non-small cell lung cancer.
      TotalpT1pT2pT3pT4pM1
      M1 attributable to additional nodules on the same side but on a different lobe from the primary tumor. NOS, not otherwise specified; NSCLC, non-small cell lung cancer.
      Total5784106631116779062415,414499580671224948180
      Adenocarcinoma NOS186346184417137710699929513101347471129
      Bronchioloalveolar141696344153227821217178
      Squamous296740418143853531164861473394966936827
      Adenosquamous5311363302916914243298
      Large-cell neuroendocrine72500029821000
      Large-cell NOS4357319669961925190545130537
      NSCLC, NOS3184615345731152269718101
      * M1 attributable to additional nodules on the same side but on a different lobe from the primary tumor. NOS, not otherwise specified; NSCLC, non-small cell lung cancer.
      TABLE 4Summary of Non-small Cell Lung Cancer Cases Analyzed by Pathologic T and Completeness of Resection
      Pathologic T
      TotalpT1pT2pT3pT4pM1
      M1 attributable to additional nodules on the same side but on a different lobe from the primary tumor.
      Any pN
       Sufficient T information15,414499580671224948180
        R013,167454869361018556109
        Non-R0100910231417935163
         R14124312210812910
         R232723413817352
         R1/R2
      No additional clarification was provided. R0, no residual disease; R1, microscopic residual disease; R2, macroscopic residual disease.
      2703615133491
        No information on completeness of resection123834581727418
      pN0
       Sufficient T information97783855479771136154
        R087273564426761923839
        Non-R033139917811112
         R1129163147341
         R210339215911
         R1/R2
      No additional clarification was provided. R0, no residual disease; R1, microscopic residual disease; R2, macroscopic residual disease.
      99205110180
       No information on completeness of resection72025243914123
      * M1 attributable to additional nodules on the same side but on a different lobe from the primary tumor.
      ** No additional clarification was provided. R0, no residual disease; R1, microscopic residual disease; R2, macroscopic residual disease.

      Validation Analysis

      The approach to validation was suggested by the validation and methodology subcommittee and is described in more detail elsewhere.

      Groome PA, Bolejack V, Crowley JJ, et al. The IASLC lung cancer staging project: validation of the proposals for revision of the T, N, and M descriptors and consequent stage grouping in the forthcoming (7th) edition of the TNM classification for lung cancer. J Thorac Oncol. In press.

      The validation analysis was performed in the general population and in the population of patients with no nodal disease. Complete and incomplete resections were included in the population for analysis of pathologic T.

      Internal Validation

      The internal validation approach was to compare results of interest among two descriptors, each divided into three strata: types of databases (consortium/surgical series versus clinical trials versus series/registries), and geographic regions (North America versus Asia/Australia versus Europe). If the direction and magnitude of effects were relatively consistent within these subgroups, the results were considered validated.
      The population for internal validation of clinical T included 5760 patients. For the validation of pathologic T, the population consisted of 15,234 patients. Table 2 shows the origins of these patients and their data sources in detail.
      Additionally, in the analysis of tumor size, the sample pT1- and pT2 N0 R0 cases with size measurements by pathologic findings were divided into a learning set of approximately two thirds (n = 4891) and a validation set of the remaining third (n = 2589). The learning set was used to develop an optimal cutpoint for tumor size, which was confirmed in the validation set. Cases were selected for the learning versus validation sets at random after balancing on attributes of size, T status, N status, region, and type of database.

      External Validation

      For external validation of the T component analysis, cases of NSCLC diagnosed from 1990 to the end of 2000 were chosen from the Surveillance, Epidemiology and End Results (SEER) registry database.

      Statistical Analysis

      Survival was measured from the date of entry (date of diagnosis for registries, date of registration for protocols) for clinically staged data and from the date of surgery for pathologically staged data; it was calculated by the Kaplan-Meier method. Prognostic groups were assessed by Cox regression analysis, using the SAS System for Windows version 9.0 PHREG procedure.
      In the derivation of tumor size cutpoints, the running log-rank statistic produced by each hypothetical cutpoint in the pN0 R0 learning set was graphed against tumor size, and the tumor size that coincided with the highest log-rank statistic was chosen as the optimal cutpoint, after rounding to the nearest whole centimeter.
      • Crowley J
      • LeBlanc M
      • Jacobson J
      • Salmon S
      Some exploratory tools for survival analysis.
      The chosen cutpoint was then tested in the pN0 R0 validation set and explored in incompletely resected cases and in all the other nodal stage groups, and also in clinically obtained measurements of tumor size. S-Plus version 7.0 was the software used to generate the log-rank statistics.

      RESULTS

      Tumor Size Cutpoints in Clinical and Pathologic T1 and T2

      When comparing overall survival between groups of patients defined by tumor size, we found that survival differences were optimized at size cutpoints of 2, 3, 5, and 7 cm. These tumor size cutpoints were chosen on the basis of pathologic measurements from completely resected cases in the learning set and were then tested in the remaining pathologic and clinical data. In the learning set of 2284 R0 patients with pT1 N0 tumors (two thirds of all such patients), the highest log-rank statistic coincided with a pathologic tumor measurement of 2.0 cm (Figure 1). For the learning set for 2607 R0 patients with pT2 N0 tumors, the highest log-rank statistic occurred at a pathologic tumor measurement of 7.3 cm, with the second-highest split at 5.0 cm (Figure 2). These four tumor size cutpoints were confirmed in the validation set of 2589 pT1- and pT2 N0 R0 cases with p values of 0.0017, <0.0001, <0.0001, and 0.0125 for each comparison between the resulting five adjacent tumor size groups, starting with the smallest tumors. In both the learning set and the validation set, tumor sizes were distributed as follows: 23% smaller than or equal to 2 cm; 23% larger than 2 cm but smaller than 3 cm; 37% larger than 3 cm but smaller than 5 cm; 11% larger than 5 cm but smaller than 7 cm; and 5% larger than 7 cm. Figure 3.
      Figure thumbnail gr1
      FIGURE 1Running log-rank statistic for pathologically measured tumor size cutpoints, according to the T1 learning set (n = 2284; two thirds of patients with R0 pT1 tumors, by UICC6 classification). A running log-rank statistic is calculated and plotted on the y-axis for each possible cutpoint on the basis of pathologically measured tumor size (x-axis). The blue lines show log-rank statistics calculated on 100 random permutations of the data. The black line shows log-rank statistics for the actual data.
      Figure thumbnail gr2
      FIGURE 2Running log-rank statistic for pathologically measured tumor size cutpoints, according to the T2 learning set (n = 2607; two thirds of patients with R0 pT2 tumors, by UICC6 classification). A running log-rank statistic is calculated and plotted on the y-axis for each possible cutpoint on the basis of pathologically measured tumor size (x-axis). The blue lines show log-rank statistics calculated on 100 random permutations of the data. The black line shows log-rank statistics for the actual data.
      Figure thumbnail gr3
      FIGURE 3Overall survival by tumor size for patients with pT1-, pT2-, or pT3 pN0 R0 tumors, using UICC6 classification.
      In all pathologically staged N0 R0 cases (learning and validation sets combined), for patients with tumors no larger than 2 cm (n = 1816), median survival was not reached. For those larger than 2 cm but smaller than 3 cm (n = 1653), survival was 113 months. For those with tumors larger than 3 cm but smaller than 5 cm (n = 2822), survival dropped to 81 months. For those with tumors larger than 5 cm but smaller than 7 cm (n = 825), survival was 56 months. For those with tumors larger than 7 cm (n =364), survival was 29 months. See FIGURE 1, FIGURE 2, FIGURE 3 and TABLE 5, TABLE 6 for details; the tables also summarize results for N0 cases irrespective of completeness of resection, and for any N status.
      TABLE 5Comparisons of Overall Survival between Tumor Size Groups for Patients with pT1, pT2, or pT3 Tumors, Using UICC6 Classification
      R0 pN0Any R pN0Any R, Any pN
      nMedian Survival (mo)5-Year Survival (%)P
      Significance value from log-rank test of equality of survival hazard functions, relative to preceding row. NR, median survival not reached.
      nMedian Survival (mo)5-Year Survival (%)p
      Significance value from log-rank test of equality of survival hazard functions, relative to preceding row. NR, median survival not reached.
      nMedian Survival (mo)5-Year Survival (%)p
      Significance value from log-rank test of equality of survival hazard functions, relative to preceding row. NR, median survival not reached.
      pT1
       ≤2 cm1816NR77195912476238911871
       >2–3 cm165311371<0.0001180010570<0.000124849162<0.0001
      pT2
       >3–5 cm28228158<0.000131758058<0.000152425649<0.0001
       >5–7 cm8255649<0.00019365749<0.000116153740<0.0001
       >7 cm3642935<0.00014263035<0.00017882228<0.0001
      pT361936410.017671132380.2739122424310.1597
      Total8099900713742
      * Significance value from log-rank test of equality of survival hazard functions, relative to preceding row. NR, median survival not reached.
      TABLE 6Comparisons of Overall Survival between Tumor Size Groups for Patients with cT1, cT2, or cT3 Tumors, Using UICC6 Classification
      cN0Any cN
      nMedian Survival (mo)5-Year Survival (%)p
      Significance value from log-rank test of equality of survival hazard functions, relative to preceding row.
      nMedian Survival (mo)5-Year Survival (%)p
      Significance value from log-rank test of equality of survival hazard functions, relative to preceding row.
      cT1
       ≤2 cm42368535185448
       >2 to ≤3 cm44552470.093254344430.1400
      cT2
       >3 to ≤5 cm134543430.1032179335390.0388
       >5 to ≤7 cm41130360.001057225320.0001
       >7 cm17317260.007625817240.0182
      cT348619290.611167719270.6482
      Total32834361
      * Significance value from log-rank test of equality of survival hazard functions, relative to preceding row.
      When clinically staged N0 cases were grouped into the five size categories as above, median survival was not significantly different between the smallest two size groups (68 vs 52 months, p = 0.09); nevertheless, comparisons between adjacent groups yielded significant survival differences at the 3-cm cutpoint (43 vs 30 months, p = 0.001) and at the 5-cm cutpoint (30 vs 17 months, p = 0.008). Survival for patients with tumors larger than 7 cm was not significantly different from cT3 tumors (17 versus 19 months, p = 0.61) (Table 6, Figure 4).
      Figure thumbnail gr4
      FIGURE 4Overall survival by tumor size for patients with cT1-, cT2, or cT3 cN0 tumors, using UICC6 classification.
      Subgroup analyses of these tumor size cutpoints within different histologic types of NSCLC yielded similar results. The differences between size categories diminished as nodal disease advanced.

      Pathologic T3, T4, and M1 by Ipsilateral Pulmonary Nodules

      In our analyses of overall survival among pathologically staged cases categorized by UICC sixth edition as T3, T4, and M1 by additional nodule (same side, different lobe), the following prognostic groups emerged: T3 (n = 1224), with median survival of 24 months; T4 exclusively by same-side nodules (n = 363), with survival of 21 months; T4 by pleural dissemination, including malignant pleural effusion or pleural nodules (n = 245), with survival of 18 months; other T4 (n = 340), with survival of 15 months; and M1 by same side/different lobe (n = 180), with survival of 18 months. In contrast to the analysis of tumor size, the primary comparisons of survival described below and shown in Figure 5 for these later-stage cases include all pathologically staged cases, irrespective of completeness of resection or nodal status. Comparisons are summarized in Table 7 for various populations (N0 R0; any R N0; and any R, any N).
      Figure thumbnail gr5
      FIGURE 5Overall survival for patients with pT3 tumors versus same-lobe nodules versus pleural dissemination by pathological finding versus other pT4 factor versus pM1 by same-side nodule, using UICC6 classification.
      TABLE 7Comparisons of Overall Survival between Patients with pT3 Tumors vs. same-lobe nodules vs. Pleural Dissemination by Pathological Finding vs. Other pT4 Factor vs. pM1 by Same-Side Nodule, Using UICC6 Classification
      R0 pN0Any R pN0Any R, Any pN
      nMedian Survival (mo)5-Year Survival (%)P
      Significance value from log-rank test of equality of survival hazard functions, relative to preceding row, except
      nMedian Survival (mo)5-Year Survival (%)p
      Significance value from log-rank test of equality of survival hazard functions, relative to preceding row, except
      nMedian Survival (mo)5-Year Survival (%)p
      Significance value from log-rank test of equality of survival hazard functions, relative to preceding row, except
      pT36193641711323812242431
      pT4 by same-lobe nodules14448450.648816046450.368536321280.2838
      pT4 by other T4 factor7225350.167911423300.005034015220.0029
      pT4 by pleural dissemination2233310.73658742240.687024518110.2904
      pM1 by same-side nodules
      pM1 by same-side nodules compared with pT4 by other T4 factor.
      3959480.1090
      Significance value from log-rank test of equality of survival hazard functions, relative to preceding row, except
      5424420.0250
      Significance value from log-rank test of equality of survival hazard functions, relative to preceding row, except
      18018220.4115
      Significance value from log-rank test of equality of survival hazard functions, relative to preceding row, except
      Total89611262352
      * Significance value from log-rank test of equality of survival hazard functions, relative to preceding row, except
      pM1 by same-side nodules compared with pT4 by other T4 factor.

      Pathologic T4 by Ipsilateral Pulmonary Nodules

      Among patients with T4 tumors by additional nodules in the same lobe, 210 (58%) were adenocarcinomas, 109 (30%) were squamous cell carcinomas, and the remaining 44 (12%) were adenosquamous, bronchioloalveolar, or unspecified NSCLC. These patients were observed to have survival similar to T3 patients (p = 0.2838). They had markedly better survival than patients staged T4 for “other― reasons (p = 0.0029)—that is, invasion of mediastinal structures and excluding pleural dissemination.

      Pathologic M1 by Ipsilateral Pulmonary Nodules in a Different Lobe from the Primary Tumor

      Survival for the 180 patients whose tumors were staged M1 by ipsilateral separate-lobe pulmonary nodules was similar to the comparator T4 group (p = 0.41), with 5-year survival rates of 22% for both groups. Their histological types were adenocarcinoma in 129 (72%) and squamous cell carcinoma in 27 (15%); the remaining 24 (13%) were adenosquamous, bronchioloalveolar carcinoma, or unspecified NSCLC.

      Clinical T4

      In practice, the discovery of same-side and, especially, same-lobe nodules is primarily a surgical rather than a clinical finding; thus, there were few patients with tumors staged cT4 (n = 17) or cM1 (n = 24) on the basis of same-side pulmonary nodules. For this reason, comparisons involving same-side nodules were not explored in detail in the clinically staged data. Conversely, malignant pleural effusions are more commonly diagnosed clinically and preclude surgery as an option. Five-year and median survival rates for the 471 patients with pleural dissemination were 2% and 8 months versus 14% and 13 months for the 418 in the comparator cT4 group (excluding same-side nodules), and survival between these two groups was statistically significantly different (p < 0.0001) (Table 8, Figure 6).
      TABLE 8Comparisons of Overall Survival between Patients Staged cT4 because of Pleural Dissemination vs. Other cT4 Factors (Excluding Same-Lobe Nodule), Using UICC6 Classification
      cN0Any cN
      nMedian Survival (mo)5-Year Survival %P
      Significance value from log-rank test of equality of survival hazard functions.
      nMedian Survival (mo)5-Year Survival %p
      Significance value from log-rank test of equality of survival hazard functions.
      cT4 by other T4 factor14421254181314
      cT4 by pleural dissemination14682<0.000147182<0.0001
      Total290889
      * Significance value from log-rank test of equality of survival hazard functions.
      Figure thumbnail gr6
      FIGURE 6Overall survival for patients with cT3 tumors versus same-lobe nodules versus pleural dissemination by clinical finding versus other cT4 factor versus cM1 by same-side nodule, using UICC6 classification.

      Other T Descriptors

      Other T2 descriptors (visceral pleural invasion and partial atelectasis), and the different T3- and T4 descriptors (except for the additional pulmonary nodule(s) in the lobe of the primary tumor) could not be evaluated, either because of the small number of patients, the inconsistent clinical and pathologic results, or lack of validation.

      Validation of Results

      Complete details of the internal and external validations of these findings are published elsewhere.

      Groome PA, Bolejack V, Crowley JJ, et al. The IASLC lung cancer staging project: validation of the proposals for revision of the T, N, and M descriptors and consequent stage grouping in the forthcoming (7th) edition of the TNM classification for lung cancer. J Thorac Oncol. In press.

      In summary, the subclassification of T1 and T2 into T1a and T1b, and T2a and T2b, respectively, driven by Asian data for pathologic size and by European data for clinical size, showed distinct differences in survival for both clinical and pathologic subgroups. These findings were consistent in most databases and in the SEER external validation, both in the overall population and in the surgical subset.
      The finding that T2 tumors larger than 7 cm were more like T3 than other T2 was observed to be both internally and externally valid. The population-based SEER data indicated more of a risk continuum by size than was seen in the project dataset, but the >7-cm group's prognosis was closer to the T3 group than it was to the rest of the T2 group.
      The influence of histologic type on the prognostic impact of tumor size was also evaluated, and the cutpoints of 2, 3, 5, and 7 cm were valid within all major cell types.
      Cases with additional nodules in the primary lobe consistently experienced better survival than other T4 cases. Nevertheless, we were not able to look at this issue using cTNM, because this T descriptor was generally only documented in the surgical data. When restricted to those treated with surgery in the SEER data, the additional nodule group's survival was better than those even with T3 disease.
      The finding that additional nodules in a different lobe of the ipsilateral lung had better prognosis than the present classification (M1) would indicate (and similar to that of T4) was driven by consortia/surgical series pathologic data that were almost all from the Asia/Australia region. This finding was also supported by the European pathologic data and the SEER registry.
      Data supporting the reclassification of pleural dissemination from T4 to M1 were driven by the European and North American series in the clinically staged analyses and by pathologic series from consortium/surgical series. These findings also were supported by the SEER data.

      DISCUSSION

      Lung cancer is responsible for more cancer deaths than any other cancer worldwide, both in men and women. Complete resection gives the highest probability of long-term remission and even cure, but only about 25% of patients are candidates for surgical treatment at the time of diagnosis. Poor performance status, comorbidity, and either locally advanced or metastatic disease exclude the rest from surgical intervention. Lung cancer classification and staging assess the anatomical extension of the tumor; this is critical to choosing a therapy and provides information on prognosis. The latest (i.e., the sixth) edition of the TNM classification of lung cancer
      was based on 5319 patients treated for primary lung cancer at The University of Texas–MD Anderson Cancer Center (4351 patients) from 1975 to 1988 or by the National Cancer Institute Cooperative Lung Cancer Study Group (968 patients) from 1977 to 1982.
      • Mountain CF
      Revisions in the international system for staging lung cancer..
      Thus, the international system for staging lung cancer is based on a national database of patients who were treated mainly in one institution. Realizing that this database was becoming relatively old and that new technology was being applied to lung cancer staging, the IASLC established an international staging committee with the purpose of collecting a large international database of patients treated for primary lung cancer, to formulate, with the agreement of the UICC and the AJCC, a new revision of the TNM classification of lung cancer, to be published in 2009. More than 100,000 patients were submitted to CRAB, the data-managing center, and more than 81,000 met all inclusion criteria.
      • Goldstraw P
      • Crowley JJ
      The International Association for the Study of Lung Cancer International Staging Project on Lung Cancer..
      These patients had been treated from 1990 to 2000. This period was chosen because no major changes had been introduced in clinical practice regarding lung cancer staging, and computed tomography scans had been widely used all over the world to stage lung cancer.
      The analyses conducted on the population of patients with information on the T descriptors revealed several findings that could be used to refine the present definitions of the T component of the TNM classification. In addition to the two size criteria, that were based on the 3-cm landmark, three more cutpoints were identified, and the five resulting size groups showed distinct survival differences. The results show that T1 tumors can be divided into two subgroups on the basis of the best cutpoints identified by the running log-rank analysis. Therefore, without altering the 3-cm landmark between T1 and T2 tumors, T1 tumors can be subdivided into two prognostic groups: those 2 cm or smaller (T1a) and those larger than 2 cm but no larger than 3 cm (T1b). This finding was validated by geographical region and database type, and by the SEER registry data. Results from other series support this division. Padilla et al.,
      • Padilla J
      • Calvo V
      • Peñalver JC
      • Sales G
      • Morcillo A
      Surgical results and prognostic factors in early non-small cell lung cancer..
      in a study on 158 patients with pT1- or pT2 NSCLC 3 cm or smaller in diameter, found that those 2 cm or smaller had better survival, and that size was a better indicator of prognosis than endobronchial invasion and visceral pleura involvement. Mulligan et al.
      • Mulligan CR
      • Meram AD
      • Proctor CD
      • Wu H
      • Zhu K
      • Marrogi AJ
      Lung cancer staging: a case for a new T definition..
      also found that tumors 2 cm or smaller in diameter had a different prognosis from that of larger tumors; they have suggested that these tumors alone should constitute T1, and that those larger than 2 cm but no larger than 4 cm, or T1 with pleural invasion, should constitute T2. In a large Japanese multicenter series of patients with T1 NSCLC, the same subgroups as those found in the analysis of the IASLC database were formed according to tumor size. Five-year survival rates for those clinically staged as T1a (1204 patients) and T1b (993 patients) were 77.5 and 69.3%, respectively (p < 0.001). For those pathologically staged as T1a (1065 patients) and T1b (886 patients), 5-year survival rates were 83.7 and 76%, respectively (p < 0.001).
      • Asamura H
      • Goya T
      • Koshiishi Y
      • et al.
      How should the TNM staging system for lung cancer be revised? A simulation based on the Japanese Lung Cancer Registry populations..
      This study also shows that T2 tumors can be divided into three subgroups of different prognosis; these could be called T2a (larger than 3 cm but no larger than 5 cm), T2b (larger than 5 cm but no larger than 7 cm), and T2c (larger than 7 cm). These cutpoints were consistent across databases and geographical regions and were supported by the SEER external validation. Other authors, on the basis of results from institutional series, have reported on the prognostic significance of the 5-cm landmark and have suggested that T2 tumors larger than 5 cm should be upgraded.
      • Carbone E
      • Asamura H
      • Takei H
      • et al.
      T2 tumors larger than five centimetres in diameter can be upgraded to T3 in non-small cell lung cancer..
      • Takeda S
      • Fukai S
      • Komatsu H
      • et al.
      Impact of large tumor size on survival after resection of pathologically node negative (pN0) non-small cell lung cancer..
      A multicenter study on clinical and pathologic size found that the prognostic landmarks were 2, 4, and 7 cm, and suggested that T2 tumors larger than 7 cm should be upgraded to T3.
      • Bronchogenic Carcinoma Cooperative Group of the Spanish Society of Pneumology and Thoracic Surgery (GCCB-S)
      Clinical tumour size and prognosis in lung cancer..
      • López-Encuentra A
      • Duque-Medina JL
      • Rami-Porta R
      • Gómez de la Cámara A
      • Ferrando P
      • Bronchogenic Carcinoma Cooperative Group of the Spanish Society of Pneumology and Thoracic Surgery
      Staging in lung cancer: is 3 cm a prognostic threshold in pathologic stage I non-small cell lung cancer? A multicentre study of 1,020 patients..
      This is in agreement with the findings of this study: T2 tumors larger than 7 cm and T3 tumors have similar prognosis. This finding has been validated in all geographic areas and databases of the IASLC for clinical or pathologic size and in the SEER registry for both.
      The results of this study also have shown that T4 tumors classified by the presence of additional nodules in the lobe of the primary tumor have better prognosis than other T4 tumors and similar prognosis to T3 tumors. This finding has been validated by the SEER registry and by all geographic areas and databases with sufficient numbers of patients. This is a very controversial point in the TNM classification, and large and small series have contradictory results. In a series of 1534 patients with completely resected NSCLC, the 5-year survival rate for 54 patients with T4 tumors without additional nodules was similar to that of 105 patients with T4 tumors by additional nodules: 34% in both cases.
      • Okumura T
      • Asamura H
      • Suzuki K
      • Kondo H
      • Tsuchiya R
      Intrapulmonary metastasis of non-small cell lung cancer: a prognostic assessment..
      Nevertheless, it has been reported from smaller series that survival of patients with T4 tumors by additional nodules can be better than that of those with stage IIIB tumors
      • Miyazawa M
      • Shiina T
      • Kurai M
      • et al.
      Assessment of the new TNM classification for resected lung cancer..
      or similar to that of patients with stage IV tumors.
      • Hosokawa Y
      • Matsuge S
      • Murakami Y
      • et al.
      Validity and controversies in the new postoperative pathologic TNM classification based on the results of surgical treatment of non-small cell lung cancer..
      These discrepancies may be attributable to the few patients with T4 tumors by additional nodules or to the difficulty in determining whether an additional nodule of the same histological type as the primary tumor is a second primary or a metastasis. Their different biologic behaviors may be responsible for the prognostic differences found in the quoted series.
      Tumors associated with malignant pleural effusion are now classified as T4 for mere taxonomic reasons: all situations within the hemithorax of the primary tumor should belong to the T component, except for nodules in another ipsilateral lobe. Nevertheless, their prognosis is much worse than that of other T4 tumors; this will be shown in a forthcoming article in the context of M1 disease. Further, they are usually treated in the same manner as patients with M1 disease. In the present study, the 5-year survival rate for patients with clinical malignant pleural effusion was 2%, and the 5-year survival rate for patients with other cT4 tumors was around 30%. Survival was better for patients with pathologic malignant pleural effusion, with 5-year survival rates of around 20%, but there were few patients in this situation, and the extent of their disease must have been very reduced and amenable to complete resection, which is not the rule with malignant pleural effusion. The poor prognosis of this situation was validated in Europe and North America and in the clinical and pathologic series of the SEER registry.
      The main limitation of this study is that most databases that have contributed to the IASLC international database were not designed to study the TNM classification. So, although more than 81,000 patients fulfilled the inclusion criteria, not all their records included information on the T descriptors that defined a certain T. Table 1 shows a summary of the number of patients with cT and pT tumors. For example, the population of surgical patients with cN0 tumors was 15,347, but only 3554 (23%) had sufficient information on T descriptors. This drop in patient numbers increased with higher T factors, and it is only 19% (110 of 582) in patients with cT4 tumors. This loss of information is even more evident in patients who did not undergo surgical treatment (Table 1). Lack of T descriptors is the reason most T2- and T3 descriptors, and all T4 descriptors (except for the additional nodule(s) in the same lobe as the primary tumor), could not be validated with the analysis of the IASLC international database. This limitation could be overcome with a prospective database with the objective of studying the TNM classification. In this database, the specific T descriptors for each tumor should be registered.
      From the analysis of the T component of the TNM classification in the IASLC international database, we can conclude that there is sufficient validated information to consider the following recommendations for changes in the seventh edition of the TNM classification of lung cancer: 1) to subclassify T1 as T1a (≤2 cm) or T1b (>2 cm to ≤3 cm); 2) to subclassify T2 as T2a (>3 cm to ≤5 cm or T2 by other factor and ≤5 cm) or T2b (>5 cm to ≤7 cm); 3) to reclassify T2 tumors >7 cm as T3; 4) to reclassify T4 tumors by additional nodule(s) in the lung (primary lobe) as T3; 5) to reclassify M1 by additional nodule(s) in the ipsilateral lung (different lobe) as T4; and 6) to reclassify pleural dissemination (malignant pleural or pericardial effusions, pleural nodules) as M1.
      The recommendations drawn from this study are solidly based. The database used is the largest ever collected for the purpose of evaluating lung cancer classification and staging. Data were collected from worldwide sources representing four distinct geographical areas. Information was collected both from highly audited datasets, such as clinical trials, and from registries, which generally are less strictly audited. Finally, the findings of this study hold when comparing different geographic regions, histologic types, and data sources, thus making the findings generalizable.
      This is one of several papers from the IASLC International Staging Committee that has the purpose of presenting our current considerations on the basis of analysis of the large dataset submitted for this project. With this publication, we hope to generate feedback from the community of physicians working in the lung cancer field to engage any positive suggestions that might allow for improvements in the present TNM classification of lung cancer.

      APPENDIX 1

      aIASLC International Staging Committee

      P. Goldstraw (chairperson), Royal Brompton Hospital, London, United Kingdom; D. Ball, Peter MacCallum Cancer Centre, Melbourne, Australia; E. Brambilla, Laboratoire de Pathologie Cellulaire, Grenoble Cedex, France; P.A. Bunn, University of Colorado Health Sciences, Denver, CO, USA; D. Carney, Mater Misericordiae Hospital, Dublin, Ireland; T. Le Chevalier, Institute Gustave Roussy, Villejuif, France; J. Crowley, Cancer Research and Biostatistics, Seattle, WA, USA; R. Ginsberg (deceased), Memorial Sloan-Kettering Cancer Center, New York, NY, USA; P. Groome, Queen’s Cancer Research Institute, Kingston, Ontario, Canada; H.H. Hansen (retired), National University Hospital, Copenhagen, Denmark; P. Van Houtte, Institute Jules Bordet, Brussels, Belgium; J-G. Im, Seoul National University Hospital, Seoul, South Korea; J.R. Jett, Mayo Clinic, Rochester, MN, USA; H. Kato (retired), Tokyo Medical University, Tokyo, Japan; T. Naruke (deceased), Saiseikai Central Hospital, Tokyo, Japan; E.F. Patz, Duke University Medical Center, Durham, NC, USA; P.E. Postmus, Free University Hospital, Amsterdam, The Netherlands; R. Rami-Porta, Hospital Mutua de Terrassa, Terrassa, Spain; V. Rusch, Memorial Sloan-Kettering Cancer Center, New York, NY, USA; J.P. Sculier, Institute Jules Bordet, Brussels, Belgium; F.A. Shepherd, University of Toronto, Toronto, Ontario, Canada; Y. Shimosato (retired), Tokyo Medical College, Tokyo, Japan; L. Sobin, Armed Forces Institute of Pathology, Washington, DC, USA; W. Travis, Memorial Sloan-Kettering Cancer Center, New York, NY, USA; M. Tsuboi, Tokyo Medical University, Tokyo, Japan; R. Tsuchiya, National Cancer Centre, Tokyo, Japan; E. Vallières, Swedish Cancer Institute, Seattle, WA, USA; Yoh Watanabe (deceased), Kanazawa Medical University, Uchinada, Japan; H. Yokomise, Kagawa University, Kagawa, Japan; and Z. Shaikh (research assistant), Royal Brompton Hospital, London, United Kingdom.

      bCancer Research and Biostatistics

      J.J. Crowley, K. Chansky, D. Giroux, and V. Bolejack, Seattle, WA, USA.

      cObservers to the Committee

      C. Kennedy, University of Sydney, Sydney, Australia; M. Krasnik, Gentofte Hospital, Copenhagen, Denmark; J.P. van Meerbeeck, University Hospital, Ghent, Belgium; J. Vansteenkiste, Leuven Lung Cancer Group, Leuven, Belgium.

      dParticipating Institutions

      O. Visser, Amsterdam Cancer Registry, Amsterdam, The Netherlands; R. Tsuchiya, T. Naruke (deceased), National Data from Japan; J.P. Van Meerbeeck, Flemish Lung Cancer Registry–VRGT, Brussels, Belgium; H. Bülzebruck, Thoraxklinik am Universitatsklinikum, Heidelberg, Germany; R. Allison and L. Tripcony, Queensland Radium Institute, Queensland, Australia; X. Wang, D. Watson, and J. Herndon, Cancer and Leukemia Group B (CALGB), USA; R.J. Stevens, Medical Research Council Clinical Trials Unit, London, United Kingdom; A. Depierre, E. Quoix, and Q. Tran, Intergroupe Francophone de Cancerologie Thoracique (IFCT), France; J.R. Jett and S. Mandrekar, North Central Cancer Treatment Group (NCCTG), USA; J.H. Schiller and R.J. Gray, Eastern Cooperative Oncology Group (ECOG), USA; J.L. Duque-Medina and A. Lopez-Encuentra, Bronchogenic Carcinoma Co-operative Group of the Spanish Society of Pneumology and Thoracic Surgery (GCCB-S), Spain; J.J. Crowley, Southwest Oncology Group (SWOG), USA; J.J. Crowley and K.M.W. Pisters, Bimodality Lung Oncology Team (BLOT), USA; T.E. Strand, Cancer Registry of Norway, Norway; S. Swann and H. Choy, Radiation Therapy Oncology Group (RTOG), USA; R. Damhuis, Rotterdam Cancer Registry, The Netherlands; R. Komaki and P. K. Allen, MD Anderson Cancer Center (MDACC-RT), USA; J.P. Sculier and M. Paesmans, European Lung Cancer Working Party (ELCWP); Y.L. Wu, Guangdong Provincial People’s Hospital, Peoples Republic of China; M. Pesek and H. Krosnarova, Faculty Hospital Plzen, Czech Republic; T. Le Chevalier and A. Dunant, International Adjuvant Lung Cancer Trial (IALT), France; B. McCaughan and C. Kennedy, University of Sydney, Sydney, Australia; F. Shepherd and M. Whitehead, National Cancer Institute of Canada (NCIC); J. Jassem and W.Ryzman, Medical University of Gdansk, Poland; G.V. Scagliotti and P. Borasio, Universita’ Degli Studi di Torino, S. Luigi Hospital, Orbassano, Italy; K.M. Fong and L. Passmore, Prince Charles Hospital, Australia; V.W. Rusch and B.J. Park, Memorial Sloan-Kettering Cancer Center, USA; H.J. Baek, Korea Cancer Centre Hospital, Seoul, South Korea; R.P. Perng, Taiwan Lung Cancer Society, Taiwan; R.C. Yung and A. Gramatikova, The Johns Hopkins University, USA; J. Vansteenkiste, Leuven Lung Cancer Group (LLCG), Belgium; C. Brambilla and M. Colonna, Grenoble University Hospital–Isere Cancer Registry, France; J. Hunt and A. Park, Western Hospital, Melbourne, Australia; J.P. Sculier and T. Berghmans, Institute of Jules Bordet, Brussels, Belgium; A.K. Cangir, Ankara University School of Medicine, Ankara, Turkey; D. Subotic, Clinical Centre of Serbia, Belgrade, Serbia; R. Rosell and V. Alberola, Spanish Lung Cancer Group (SLCG), Spain; A.A. Vaporciyan and A.M. Correa, MD Anderson Cancer Center–Thoracic and Cardiovascular Surgery (MDACC-TCVS), USA; J. P. Pignon, T. Le Chevalier, and R. Komaki, Institut Gustave Roussy (IGR), France; T. Orlowski, Institute of Lung Diseases, Warsaw, Poland; D. Ball and J. Matthews, Peter MacCallum Cancer Centre, Melbourne, Australia; M. Tsao, Princess Margaret Hospital, Toronto, Canada; S. Darwish, Policlinic of Perugia, Italy; H.I. Pass and T. Stevens, Karmanos Cancer Institute, Wayne State University, USA; G. Wright, St Vincent’s Hospital, Victoria, Australia; and C. Legrand and J.P. van Meerbeeck, European Organisation for Research and Treatment of Cancer (EORTC), Brussels, Belgium.

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