First-line dacomitinib (PF-00299804), an irreversible pan-HER tyrosine kinase inhibitor, for patients with EGFR-mutant lung cancers.

Abstract

7530 Background: Dacomitinib irreversibly inhibits EGFR, HER2 and HER4, and showed superior activity vs. reversible EGFR tyrosine kinase inhibitors in EGFR-mutant lung cancer models, including resistant forms. This open-label Phase II study evaluates dacomitinib as 1st-line treatment (tx) for patients (pts) with lung cancers. Pts with sensitizing EGFR deletions/mutations in exons 19 or 21 are reported here. Methods: Pts had stage IIIB/IV adenocarcinoma, no prior systemic tx, had smoked <10 pack years (none within 15 years of enrollment) or had known EGFR mutation. Pts received dacomitinib orally once daily continuously at 45 mg, or 30 mg with the option to escalate to 45 mg; evaluation was every 28 days. Endpoints included progression-free survival rate at 4 months (PFS at 4M, primary); PFS, and partial response (PR) rate. Results: 92 pts enrolled; 47 had EGFR mutation in exons 19 (n=25) or 21 (n=22), 33 were female and 27 Asian. 34/46 evaluable pts with EGFR exon 19 or 21 mutations had a PR (PR rate = 74%; 95% CI: 59–86; exon 19 = 72%; exon 21 = 76%). PR rates and preliminary PFS were not significantly different for exons 19 and 21. Preliminary PFS at 4M was 96% (95% CI: 84–99), preliminary PFS rate at 1 year was 77% (95% CI: 61–87) and preliminary median PFS was 17 months (95% CI: 13–24). Median tx duration was 13.1 months. For pts with EGFR wild-type lung cancers, PR and PFS at 4M rates were 7% (n=14; 95% CI: 0–34) and 33% (n=14; 95% CI: 11–58), respectively, and for pts with EGFR unknown lung cancers, 46% (n=22; 95% CI: 24–68) and 68% (n=24; 95% CI: 45– 83), respectively. 7 pts had lung cancers with non-sensitizing EGFR mutations; 2 had a PR and 3 SD. For all 92 pts, common side effects included dermatitis acneiform (grade 3/4 = 17%/0) and diarrhea (14%/0). 3/46 pts with EGFR exon 19 or 21 mutations discontinued tx due to drug-related toxicity. Conclusions: 74% of pts in this cohort with EGFR exon 19 or 21 mutant lung cancers experienced PRs with 1st-line dacomitinib; preliminary PFS rate was 77% at 1 year; preliminary median PFS was 17 months; further research is planned in this pt population. As dacomitinib is well tolerated, with preclinical activity against HER2, a cohort of pts with HER2 mutant lung cancers is recruiting.