Phase II trial of neoadjuvant osimertinib for surgically resectable EGFR-mutated non-small cell lung cancer.

8508 Background: Osimertinib is a third-generation EGFR tyrosine kinase inhibitor (TKI) effective in treating advanced EGFR-mutated non-small cell lung cancer (NSCLC). Adjuvant osimertinib significantly decreases disease recurrence in stage IB-IIIA EGFR-mutated NSCLC. However, the benefit of neoadjuvant osimertinib prior to surgical resection remains unknown. Methods: This was a multi-institutional phase II trial of neoadjuvant osimertinib for patients with surgically resectable stage I-IIIA (AJCC V7) EGFR-mutated (L858R or exon 19 deletion) NSCLC (NCT03433469). Patients received osimertinib 80 mg orally daily for up to two 28-day cycles prior to surgical resection. The primary endpoint was major pathological response (mPR) rate (≤10% residual viable tumor). 27 evaluable patients provide 87% power to detect a mPR rate of 50% with α = 0.05. Secondary endpoints included pathological response (PR) rate (≤50% residual viable tumor), pathological complete response (pCR) rate, unconfirmed objective response rate (ORR), rate of lymph node downstaging, unanticipated delays to surgery, surgical complication rate, disease-free survival (DFS), overall survival (OS), safety, and tumor mutational profile. Results: A total of 27 patients with early-stage (8 stage IA/B, 10 stage IIA/B, 9 stage IIIA) EGFR-mutated (11 exon 19 del, 16 L858R) NSCLC were treated with neoadjuvant osimertinib for a median 56 days prior to surgical resection. 24 (89%) patients underwent subsequent surgery; 3 (11%) patients were converted to definitive chemoradiotherapy. The mPR rate was 15% (4/27 patients) by intention-to-treat analysis. The PR rate was 48% (13/27). No pCR’s were observed. Partial responses by radiography were observed in 52% (14/27) of patients and stable disease in 44% (12/27) of patients. Lymph node downstaging was achieved in 44% (4/9) of patients with positive lymph nodes. Median DFS after surgical resection was 32 months (95% CI 26-not reached) with a median follow-up of 11 months. OS data are immature. Significant adverse events occurred in 3 patients with grade 2 (G2) dyspnea, grade 3 (G3) pulmonary embolism, and G3 atrial fibrillation. One patient developed G2 treatment-related pneumonitis that resolved without steroids. Perioperative complications occurred in 38% (9/24) of patients; most involved rapidly reversible postoperative G2 atrial fibrillation (6/9) unrelated to study drug. Tumors were evaluable for genetic alterations from 16 patients. 4/6 patients who did not achieve a PR had tumors that harbored loss of function mutations in RBM10 as compared to 0/10 patients who achieved a PR (p < 0.01). Conclusions: Neoadjuvant osimertinib in surgically resectable EGFR-mutated NSCLC achieved a 15% mPR, which did not meet the primary endpoint. Treatment was safe and may induce pathological responses and lymph node-downstaging of disease. Co-mutations in RBM10 may limit response. Clinical trial information: NCT03433469 .