A phase I dose escalation study evaluating the safety and tolerability of a novel anti-HER2 antibody-drug conjugate (PF-06804103) in patients with HER2-positive solid tumors.

Abstract

1039 Background: PF-06804103 is an anti-HER2 immunoglobulin G1 antibody-drug conjugate (ADC), comprising an anti-HER2 monoclonal antibody conjugated with a cleavable linker to the cytotoxic agent Aur0101. PF-06804103 demonstrated strong activity in low to high HER2-expressing preclinical tumor models. In this study, the safety and tolerability of PF-06804103 was assessed in patients with advanced breast cancer (BC) or gastric cancer (GC). Methods: This multi-center, open-label, first-in-patient, phase I study (NCT03284723) has two parts: dose escalation (Part 1) and dose expansion (Part 2). In Part 1, groups of adult patients (pts) with HER2+ BC or HER2+ GC, who are resistant or intolerant to standard therapy or for which no standard therapy is available, received PF-06804103 intravenously once every 21 days (Q3W); dosage was escalated per cohort. Primary objectives were to evaluate the safety and tolerability of PF-06804103, characterize its dose-limiting toxicities (DLTs), and determine the recommended phase 2 dose. Response was assessed using RECIST v1.1. Objective response rate (ORR) was calculated for response-evaluable pts with target lesions at baseline and ≥1 post-baseline assessment (including unconfirmed responses). Results: A total of 35 pts (BC: n = 20; GC: n = 15) received PF-06804103 at escalating dose levels (0.15 mg/kg: n = 2; 0.5 mg/kg: n = 2; 1.2 mg/kg: n = 2; 2 mg/kg: n = 4; 3 mg/kg: n = 10; 4 mg/kg: n = 9; 5 mg/kg: n = 6). The median (range) number of prior therapies was 6 (3–18) and 3 (1–6) for BC and GC groups, respectively (all pts had prior HER2-targeted therapy). The 3 most common, drug-related adverse events (any grade) were alopecia (n = 17, 48.6%), fatigue (n = 15, 42.9%), and neuropathy (n = 9, 25.7%). DLTs (mostly grade 3) occurred in 3 pts and included arthralgia, neuropathy, myalgia, fatigue, and osteomuscular pain. Preliminary ORR in the patients treated with doses ≥3mg/kg was 52.4% (11/21). Conclusions: The PF-06804103 ADC demonstrated manageable toxicity and promising anti-tumor activity in this small, heavily pretreated study population. Clinical trial information: NCT03284723 .