Among patients with metastatic colorectal cancer, the addition of the targeted therapy Vectibix® (panitumumab) to chemotherapy delayed cancer progression. This benefit was only observed in patients whose tumors did not contain a mutation in the KRAS gene. These results were made available in a press release from Amgen.

Vectibix is a new targeted therapy that binds to specific targets on cancer cells. Vectibix targets the epidermal growth factor receptor (EGFR), a biologic pathway that is involved in the growth and spread of cancer. Vectibix, which is FDA approved, is often used in combination with chemotherapy for the treatment of colorectal cancer. Vectibix appears to benefit only those patients who cancers do not contain a mutation in a gene known as KRAS. KRAS mutations occur in an estimated 40-50% of metastatic colorectal cancers and can be identified by testing a sample of tumor tissue.

To evaluate the effectiveness of Vectibix in the initial (first-line) treatment of metastatic colorectal cancer, researchers conducted a Phase III clinical trial known as PRIME (Panitumumab Randomized trial In combination with chemotherapy for Metastatic colorectal cancer to determine Efficacy). The study enrolled 1,183 patients. Study participants were assigned to receive treatment with FOLFOX chemotherapy alone or FOLFOX plus Vectibix.

• Among patients without KRAS mutations, the addition of Vectibix significantly improved progression-free survival. In contrast, among patients with KRAS mutations, the addition of Vectibix worsened progression-free survival.
• Side effects of Vectibix included skin rash, low magnesium levels, and diarrhea.

Comments: The results of this study suggest that the addition of the targeted therapy Vectibix to first-line chemotherapy improves progression-free survival among patients with metastatic colorectal cancer. The benefit only applies to patients whose tumors do not contain KRAS mutations. Full results from this study are expected to be presented at an upcoming medical meeting.

Reference: Amgen News Release. Vectibix® In Combination With Chemotherapy Significantly Improved Progression-Free Survival In First-Line Metastatic Colorectal Cancer. Available at: http://www.amgen.com/media/media_pr_detail.jsp?year=2009&releaseID=1318284 Accessed August 10, 2009.