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| |  Formation of Panitumumab Antibodies Rare, No Impact on Efficacy: Presented at ASCO-GI By Ed Susman ORLANDO, Fla -- January 25, 2010 -- Formation of antibodies to the targeted therapy panitumumab occur rarely among patients being treated for metastatic colorectal cancer but even when these antibodies do appear they did not seem to affect outcomes, researchers said here at the 2010 Gastrointestinal Cancers Symposium (ASCO-GI). Researchers combined data from 2 phase 3 studies on panitumumab and found that the development of new neutralising antibodies occurred in 18 of 971 patients. “Since panitumumab is a fully-human compound, we really didn’t expect to see a lot of neutralising antibodies,” said Marta Starcevic, PhD, Amgen, Thousand Oaks, California, on January 24. “And we were unable to see that the formation of these antibodies has any impact on outcomes.” One of the studies examined the use of second-line panitumumab 6 mg/kg plus FOLFIRI (irinotecan, leucovorin, and 5-fluorouracil) compared with FOLFIRI alone every 2 weeks until disease progression occurred or the patient developed intolerability to the treatment. The second study compared panitumumab 6 mg/kg plus FOLFOX4 (oxaliplatin, leucovorin, and 5-fluorouracil) with FOLFOX4 alone. Both studies were randomised, multicentre, phase 3 trials of patients with metastatic colorectal cancer. Depending on the type of test for measuring antibodies that was used, or whether the patients’ tumours expressed mutated or wild-type genetic factors, new neutralising antibodies were identified in 4 of 501 patients treated with panitumumab in the FOLFIRI trial and in 14 of 470 patients treated with panitumumab in the FOLFOX4 trial. “The incidence of anti-panitumumab antibodies was similar in patients with tumours expressing wild type of mutant KRAS,” said Dr. Starcevic. “No evidence of an altered safety profile was found in patients who tested positive for anti-panitumumab antibodies.” She did note, however, that a full analysis of whether the neutralising antibodies impacted efficacy was difficulty to perform because so few of the patients developed those antibodies. The researchers performed the antibody analyses using serum samples from the patients enrolled in the studies. Funding for this study was provided by Amgen. The 2010 Gastrointestinal Cancers Symposium is sponsored by the American Gastroenterological Association Institute, the American Society of Clinical Oncology, the American Society for Therapeutic Radiation Oncology, and the Society of Surgical Oncology. [Presentation title: Panitumumab Immunogenicity in Two Phase III Trials of Patients With Metastatic Colorectal Cancer (mCRC) Treated With Panitumumab Plus FOLFIRI or FOLFOX4. Abstract 433]
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