Panitumumab Antitumor Activity In Patients (Pts) With Metastatic Colorectal Cancer (Mcrc) Expressing Low (1-9%) Or Negative (< 1%) Levels Of Epidermal Growth Factor Receptor (Egfr).

3547 Background: Panitumumab is a fully human monoclonal antibody directed against EGFr. We investigated the antitumor activity of panitumumab in pts with mCRC who failed prior therapy and had low or negative EGFr tumor expression. Methods: In this multicenter, phase 2 study of 150 planned pts, pts had documentation of disease progression (PD) during or after adequate doses of fluoropyrimidine, irinotecan, and oxaliplatin (centrally confirmed refractory disease [CCRD]), 2–3 prior regimens, ECOG score 0–2, and low or negative EGFr staining (by IHC) in evaluable tumor cells. Pts received panitumumab at 6 mg/kg Q2W until PD or drug intolerability. Tumor assessments (modified WHO, blinded central review) were taken periodically from wk 8 until PD. Endpoints were objective response (OR) through wk 16 (+ ≥ 4 wk confirmation; primary) and OR throughout study, response duration, progression-free survival (PFS) time, survival time, and safety (secondary). Results: In this interim analysis (6/05), 88 pts were enrol...