Panitumumab Effective in Heavily Pretreated Metastatic CRC

ORLANDO-Panitumumab, which binds to the epidermal growth factor receptor (EGFR), "demonstrated encouraging antitumor activity in patients with metastatic carcinoma of the colon or rectum who failed standard chemotherapy," Imitiaz Malik, MD, said (abstract 3520). Dr. Malik reported data from an ongoing phase II study of 148 patients who had treatment-resistant metastatic colorectal cancer (CRC) despite prior treatment with a fluoropyrimidine (± leucovorin) and either irinotecan(Drug information on irinotecan) (Camptosar) or oxaliplatin(Drug information on oxaliplatin) (Eloxatin), or both. Endpoints included tumor response (according to RECIST criteria), time to disease progression, survival, and safety. Patients were stratified according EGFR status. Cohort A included pa- tients with EGFR staining of 2+ or 3+ in at least 10% of tumor cells. Cohort B included patients with EGFR staining of the sum of 1+, 2+, and 3+ in 10% of tumor cells but with the sum of 2+ and 3+ in < 10% of tumor cells. Panitumumab was given intravenously at 2.5 mg/kg once weekly in 8- week cycles. Treatment continued until disease progression or unacceptable toxicity occurred. Mature Data Confirm Previous Finding Panitumumab was active in both patient cohorts (Table 1). The four most frequent grade 3 or 4 side effects were rash, fatigue, vomiting, nausea, and pruritus. One hundred forty-one patients (95%) had skin toxicity, including 5% that were grade 3. Dr. Malik said that one infusion-related grade 3 adverse event, which did not require dose modification, was reported, and there were no human antihuman antibodies in the 145 patients tested. "These mature data confirm previously reported safety and response findings and provide encouraging survival data in patients with metastatic CRC who have failed multiple lines of standard chemotherapy," Dr. Malik said. "Median duration of response was 18.1 weeks by central review, and response was seen in patients receiving up to four lines of prior therapy. Also, there appeared to be no significant differences in all efficacy parameters assessed between cohort A and cohort B." Dr. Malik said that panitumumab is currently being studied in a phase II trial as third- or fourth-line treatment in patients with metastatic CRC whose tumors have low or negative EGFR expression. The antibody is also in randomized trials in combination with bevacizumab(Drug information on bevacizumab) (Avastin) and chemotherapy as first-line therapy. This study was supported by Amgen, Inc.