RATIONALE: Studying samples of tissue in the laboratory from patients who received cetuximab may help doctors understand and predict how well patients will respond to treatment.

PURPOSE: This research study is studying biomarkers in predicting response to cetuximab in patients with advanced colorectal cancer.

OBJECTIVES:

Primary

• To determine, among patients with advanced CRC, whether the effect of treatment (cetuximab vs bevacizumab) on progression-free survival (PFS) depends on tumor BRAF V600E mutational status.

Secondary

• To study the relationships between tumor BRAF V600E mutational status, OS, and tumor response.

OUTLINE: This is a multicenter study.

Previously collected formalin-fixed and paraffin-embedded baseline tumor samples are analyzed for BRAF V600E mutation. Mutation status is correlated with clinical response and outcome data from patients enrolled on CALGB-C80405.

DISEASE CHARACTERISTICS:

• Participation in CALGB-C80405

  • Have KRAS WT or KRAS mut tumor

  • Randomized to treatment with either bevacizumab or cetuximab alone

    • Patients randomized to the combination therapy are not eligible

• Available specimens at the PCO for BRAF mutation detection

• Patient consent for use of samples

Patients previously enrolled on CALGB-C80405 who have KRAS WT or KRAS mut tumor and have been randomized to treatment with either bevacizumab or cetuximab alone in a primary care clinic setting.