Studying Biomarkers in Tumor Tissue and Blood Samples From Patients Undergoing Chemotherapy and Radiation Therapy for Stage II or Stage III Rectal Cancer That Can Be Removed By Surgery

RATIONALE: Studying samples of tumor tissue and blood from patients with cancer in the laboratory may help doctors learn more about changes that occur in DNA and identify biomarkers related to cancer. It may also help doctors predict how patients respond to treatment.
PURPOSE: This phase I trial is studying biomarkers in tumor tissue and blood samples from patients undergoing chemotherapy and radiation therapy for stage II or stage III rectal cancer that can be removed by surgery.