Panitumumab activity in metastatic colorectal cancer (mCRC) patients (pts) with low or negative tumor epidermal growth factor receptor (EGFr) levels: An updated analysis

Abstract

4082 Background: Panitumumab, a fully human monoclonal antibody against EGFr, is approved for EGFr-expressing mCRC pts with disease progression (PD) on or after fluoropyrimidine-, oxaliplatin-, and irinotecan-containing chemotherapy. However, the predictive value of EGFr tumor-membrane staining as measured by immunohistochemistry (IHC) is undetermined. Methods: This multicenter, single arm, phase 2 study enrolled pts with documented PD during or after fluoropyrimidine and adequate doses of irinotecan and oxaliplatin, and within 6 months after the most recent chemotherapy regimen (determined by an independent eligibility review committee [IERC]), 2–3 prior regimens, and low (1%-9%) or negative (<1%) EGFr tumor membrane staining (by IHC). Pts received panitumumab 6mg/kg Q2W until PD or intolerability. Tumor assessments (modified WHO, blinded central review) were performed every 8 weeks until PD or discontinuation. Endpoints were objective response rate (ORR) through wk 16 (+ =4 wk confirmation; primary), overall ORR, response duration, progression-free survival (PFS), and safety (secondary). Results: In this interim analysis, 91 pts had =20 wks of potential follow-up and comprised the IERC efficacy set; 118 pts comprised the evaluable safety set (=20 wks potential follow-up). In the IERC efficacy set, 57% were male, 86% were white, and median age (range) was 61 (26–85) years. ORR through week 16 is shown; overall ORR was the same ( Table ). The most common adverse events (all, grade 3/4) were dermatitis acneiform (72%, 6%), erythema (69%, 6%), pruritus (65%, 4%), and hypomagnesaemia by lab values (53%, 10%). Four pts (3%) had an infusion reaction per investigator (1 was grade 3). Conclusions: This analysis confirms earlier findings that panitumumab has anti-tumor activity in pts with low or undetectable EGFr tumor membrane levels as measured by IHC. This study has completed enrollment, and updated data will be presented. [Table: see text] No significant financial relationships to disclose.