Daiichi Sankyo Company, Limited announced new data of patritumab deruxtecan (HER3-DXd), a HER3 directed antibody drug
conjugate (ADC), demonstrated preliminary evidence of clinically meaningful and durable tumor response in patients with locally advanced or metastatic TKI-resistant, EGFR-mutated non-small cell lung cancer (NSCLC). These extended follow-up data from the dose escalation portion and one expansion cohort of a phase 1 study of patritumab deruxtecan were presented during an oral presentation (Abstract #9007) at the 2021 American Society of Clinical Oncology (#ASCO21) Virtual Scientific Program.
While the efficacy of targeted therapy with EGFR TKIs is well-established in the treatment of patients with advanced EGFR-mutated NSCLC, the development of a broad range of resistance mechanisms commonly leads to disease progression. Subsequent salvage therapies after EGFR TKI and platinum-based chemotherapy have limited efficacy with progression-free survival (PFS) of approximately 2.8 to 3.2 months. New treatment approaches are needed to overcome resistance and improve survival in these patients. An objective response rate (ORR), as assessed by blinded central review, was 39% (CI 95%; 26-52%) in 57 evaluable patients treated with patritumab deruxtecan (5.6 mg/kg). One confirmed complete response and 21 partial responses were observed. The disease control rate was 72% (CI 95%; 59-83%). After a median follow-up of 10.2 months (range, 5.2-19.9 months), the estimated median duration of response was 6.9 months (CI 95%; range, 3.1-NE months) and the estimated median PFS was 8.2 months (CI 95%; range, 4.4-8.3 months). Confirmed responses were observed in patients across a spectrum of baseline tumor HER3 membrane expression levels, EGFR activating mutations and EGFR TKI resistance mechanisms, including EGFR activating mutations (Ex19del, L858R, G719Y), other EGFR mutations (T790M, C797S, Ex20ins), amplifications (EGFR, CCNE1, MET) and non-EGFR mutations and fusions (MET, KRAS). A subgroup of patients treated with osimertinib and platinum-based chemotherapy (n=44) prior to enrollment in the study demonstrated similar efficacy. An ORR of 39% (CI 95%; 24-55%) and PFS of 8.2 months (CI 95%; 4.0-NE) was observed in this subgroup. Additionally, the confirmed ORR and median PFS were similar in patients with or without a history of brain metastases.