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Malignant Pleural Mesothelioma Localized in the Thoracic Wall

      Malignant pleural mesothelioma (MPM) usually shows a diffuse pattern of growth over the pleural surfaces. We present an unusual case of MPM that was localized and had spread outside the thoracic wall.

      CASE REPORT

      A 65-year-old man was referred to our hospital because of dry cough. He was a never smoker and worked at a chemical fiber factory where he was exposed to asbestos for 40 years. Physical examination revealed that the skin over the left subclavian area was swollen but without tenderness or redness.
      A chest radiograph showed hypolucency on the left side. A computed tomographic scan of the chest showed a 7-cm diameter tumor on the left anterior chest wall surrounding the second rib (Fig. 1). No pleural plaque, effusion, or lymphadenopathy was detected. Fluorodeoxyglucose positron emission tomographic computed tomographic imaging showed the accumulation of fluorodeoxyglucose in the tumor with the maximum standardized uptake value of 15.1 without accumulation in any other organ. The diagnosis of MPM, epithelioid type, was made from a percutaneous needle-biopsy specimen. Thoracoscopic exploration showed that the tumor was covered with parietal pleura, and no dissemination was found on the pleura. The tumor and the involved first, second, and the third ribs were removed with curative intent. The resected specimen revealed cubiform tumor cells; some of which were forming a papillary tubular structure (Fig. 2A). Immunohistochemical analyses demonstrated that the tumor cells were positive for calretinin (Fig. 2B), D2–40, Wilms’ tumor 1, thrombomodulin, cytokeratin 5/6, and epithelial membrane antigen, and negative for carcinoembryonic antigen (Fig. 2C), thyroid transcription factor, and napsin A. The diagnosis was confirmed as epithelioid type MPM. Detailed investigation of the specimen showed that the parietal pleura was involved with tumor cells (Fig. 3), indicating that the tumor originated from the parietal pleura. Six months later, he had a local recurrence and underwent radiotherapy and systemic chemotherapy.
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      FIGURE 1Computed tomographic scan of the chest at the time of diagnosis showing (A) coronal and (B) horizontal views of a tumor on the left anterior chest wall.
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      FIGURE 2A, Microscopic examination of the biopsy specimen showed cubiform tumor cells; some of the cells formed papillary tubular structures consistent with malignant mesothelioma (hematoxylin-eosin, 40 ×). B, Immunohistochemical analysis indicated positive expression of calretinin (40 ×) and (C) negative expression of carcinoembryonic antigen (40 ×).
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      FIGURE 3Microscopic examination of the biopsy specimen showed that the parietal pleural was involved with tumor cell (arrows), indicating that the tumor originated from the parietal pleura.

      DISCUSSION

      In the current case, a patient presented with MPM that localized and spread outside the thoracic wall. The tumor was initially suspected to be a soft-tissue neoplasm, osteoblastic metastatic tumor, or malignant lymphoma. The pathological diagnosis of MPM was determined from a percutaneous needle-biopsy specimen. Thoracoscopic exploration showed that the tumor was covered with parietal pleura without dissemination into the pleura, an unusual pattern of MPM progression.
      MPM is classified in diffuse MPM or localized (LMPM). LMPM is uncommon and characterized by a sharply circumscribed tumor of the seromal membranes with the microscopic appearance of diffuse malignant mesothelioma, but without any evidence of diffuse spread.
      • Allen TC
      • Cagle PT
      • Churg AM
      • et al.
      Localized malignant mesothelioma.
      It was formerly considered a benign variant of mesothelioma,
      • Robinson LA
      • Reilly RB
      Localized pleural mesothelioma. The clinical spectrum.
      solitary fibrous tumor,
      • Crotty TB
      • Myers JL
      • Katzenstein AL
      • Tazelaar HD
      • Swensen SJ
      • Churg A
      Localized malignant mesothelioma. A clinicopathologic and flow cytometric study.
      or other neoplasms, but is now defined as having the microscopic, histochemical, immunohistochemical, and ultrastructural features of diffuse MPM. However, little is known about the frequency and clinical behavior of LMPM.
      The tumor in the current case was grossly localized in the thoracic wall. Detailed pathological analyses showed that the parietal pleura were involved with tumor cells, but diffuse pleural spread was not determined; therefore, we regard the current case as LMPM. LMPM should be considered a thoracic tumor that is localized and has spread outside the thoracic wall.

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