Chemoresistance remains an obstacle in treating people with metastatic colorectal cancer (mCRC). Studying samples of blood and tumor tissue in the laboratory from patients with mCRC receiving chemotherapy may help doctors understand the effect of chemotherapy on biomarkers. It may also help doctors predict how patients will respond to treatment. In this study, we aimed to evaluate biomarkers in chemotherapy regimens for first-line chemotherapy for mCRC.

Inclusion Criteria Histologically confirmed metastatic colorectal cancer Unresectable metastatic disease must be confirmed histologically if > 2 years since primary diagnosis Measurable metastatic disease > 1 cm by spiral CT scan or > 2 cm by other methods Scheduled to receive first-line chemotherapy for metastatic disease Chemotherapy must include fluorouracil, capecitabine, irinotecan hydrochloride, or oxaliplatin Exclusion Criteria Inadequate or unusable tissue as the only tissue available Brain metastases or meningeal disease Contraindication to chemotherapy Pregnant or nursing Other severe pathology that is likely to worsen during therapy Dementia or severely impaired mental condition Geographical or psychological reasons that would preclude treatment

Histologically confirmed metastatic colorectal cancer