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OA02.06 A Phase II Trial of Poziotinib in EGFR and HER2 exon 20 Mutant Non-Small Cell Lung Cancer (NSCLC)

      Background

      Insertions/mutations in exon 20 of EGFR or HER2 occur in ∼3% of all lung adenocarcinomas. These alterations are characterized by primary resistance to tyrosine kinase inhibitors (TKIs) with response rates of <12%. We previously showed that exon 20 insertions restrict the size of drug-binding pocket, limiting binding of most available TKIs. However, poziotinib can potentially circumvent these steric changes due to its smaller, flexible structure and is a potent inhibitor of EGFR and HER2 exon 20 mutants (Robichaux et al. Nat Med, 2018). Herein, we report the results of an investigator-initiated study of poziotinib in EGFR and HER2 exon 20 mutant NSCLC (NCT03066206).

      Method

      Patients ≥18yrs with metastatic NSCLC bearing mutations/insertions in EGFR or HER2 exon 20 (except EGFR T790M) were eligible. Unlimited prior systemic and targeted therapies were permitted. Poziotinib 16mg PO daily was administered until progression, death, or withdrawal. The primary endpoint was objective response rate (ORR) based on RECIST v1.1. Response was evaluated every eight weeks. A Bayesian design was used with a plan to enroll patients in cohorts of 10 and to terminate the study if ORR was ≤20%. Secondary endpoints included DCR, PFS, OS and safety

      Result

      As of May 3, 2018, the planned EGFR cohort of 50 patients was fully enrolled, and 40 patients were evaluated for response. 65.1% of patients had received at least two prior lines of therapy for metastatic disease. 60% of patients had ≥grade 3 adverse events; most common were skin-rash (27.5%) and diarrhea (12.5%). 45.0% of patients required dose reduction to 12mg, while 17.5% required dose reduction to 8mg. One patient stopped treatment due to grade 3 skin rash. ORR at eight weeks was 58% (95%-CI 40.9-73.0) and the DCR was 90% (95%-CI 76.3-97.2). Among 23 patients who achieved partial response, 15 responses were confirmed with subsequent scans, five responses were unconfirmed, and three patients are pending confirmation. Responses were observed in 8/13 (62%) patients that were previously treated with TKI. Median PFS was 5.6mo (95%-CI 5.06-NA). Furthermore, 13 patients were enrolled in HER2 cohort. Toxicities were similar to EGFR cohort except one case of grade 5 pneumonitis, assessed to be possibly drug related. Twelve patients were evaluated for response with ORR of 50% (95% CI 21.1-78.9) at eight weeks and DCR of 83%.

      Conclusion

      In heavily pre-treated population with EGFR and HER2 exon 20 mutant NSCLC, poziotinib demonstrated encouraging antitumor activity in both TKI-naive and -refractory patients, and manageable toxicity profile.

      Keywords

      EGFR Exon 20 insertion, Novel therapy, Targeted therapy