mCRC treatment induced response in 17% of patients with nonmutated KRAS compared to none with the mutated form.

Amgen reported that in metastatic colorectal cancer (mCRC) patients who have failed chemotherapy, the efficacy of Vectibix™ monotherapy is confined to those with nonmutated KRAS tumors. In such patients, Vectibix increased progression-free survival (PFS) and had an impact on quality of life (QoL) and disease-related symptoms, according to the company.

The data was generated from a biomarker analysis of a Phase III, randomized, controlled clinical trial that investigated the treatment effect of Vectibix monotherapy plus best supportive care (BSC) versus BSC alone in patients with mCRC.

Of the 463 randomized patients in the trial, 427 had available KRAS data, and 57  had tumors with normal, nonmutated KRAS. In the group of patients with nonmutated KRAS that received Vectibix, 17% responded to treatment and 34% reported stable disease, according to Amgen. There were no responders in the group of patients treated with Vectibix that had mutated KRAS. Stable disease was reported in 12% of these patients.

Additional endpoints of this analysis examined overall survival by KRAS status and treatment. Comparing the nonmutated and mutated treatment arms, overall survival was longer in patients with nonmutated KRAS, the company notes. No differences in overall survival were observed between Vectibix and BSC in either KRAS subgroup, potentially due to a high rate of crossover from BSC to Vectibix after progression and similar efficacy of Vectibix in these patients, reports the company.

Results from this study will be presented on January 26 at the “2008 American Society of Clinical Oncology Gastrointestinal Cancers Symposium.”

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