Panitumumab antitumor activity in patients (pts) with metastatic colorectal cancer (mCRC) expressing ≥ 10% epidermal growth factor receptor (EGFr)

Abstract

3548 Background: Panitumumab is a fully human monoclonal antibody directed against EGFr. We investigated panitumumab antitumor activity in pts who failed prior therapy and had EGFr tumor expression levels ≥ 10%. Methods: In this multicenter, phase 2 study of 300 planned pts, pts had documentation of disease progression (PD) during or following adequate doses of fluoropyrimidine, irinotecan, and oxaliplatin (centrally confirmed refractory disease [CCRD]), 2–3 prior regimens, ECOG score 0–2, and EGFr staining (by IHC) in ≥ 10% of evaluable tumor cells. Pts received panitumumab at 6 mg/kg Q2W until PD. Tumor assessments (modified WHO, blinded central review) were taken periodically from wk 8–48 until PD. Study endpoints were objective response rate (ORR) at wk 16 (+ ≥ 4 wk confirmation; primary) and ORR throughout study, response duration, progression-free survival (PFS) time, survival time, and safety (secondary). Results: In this interim analysis (5/05), 91 enrolled pts received ≥ 1 dose of panitumumab (safety set); 39 had ≥ 20 wks before the cutoff and CCRD (efficacy set). The efficacy set consisted of 23M/16W, mean (SD) age of 58.6 (10.1) years, 82% white, 95% ECOG ≤ 1, 74% colon cancer and 26% rectal cancer; all had ≥ 2 prior regimens (equivalent characteristics for safety set). At wk 16, 3 (8%) had a partial response, 8 (21%) had stable disease, and 19 (49%) had PD as best OR (9 not done/unevaluable). At the time of this interim analysis, response durations were 12.4, 13.2, and 14.0 wks. In the safety set, 96% had at least 1 treatment-related adverse event (24% grade [gr] 3, 1% gr 4, 1% gr 5). Integument and eye toxicities were: 96% skin, 30% nail, 8% eye, 5% hair, and 7% chelitis. 25 (27%) had diarrhea (3 gr 3); 11 (12%) had hypomagnesemia (3 gr 3/4). One pt had a gr 3 hypersensitivity reaction considered related to panitumumab, received medication, and the event resolved; this pt continued treatment with premedication; no further reactions occurred. In 66 pts with both a baseline and postdose sample, no human anti-human antibodies to panitumumab were detected.Additional data will be presented. Conclusions: Panitumumab has antitumor activity and is well tolerated in pts with EGFr tumor expression levels ≥ 10% who failed standard chemotherapy. [Table: see text]