Growth Factor Levels in the Blood of Patients Undergoing Radiation Therapy for Epithelial Cancer

RATIONALE: Measuring levels of transforming growth factor-beta (TGF-beta) in the blood of patients with epithelial cancers (head and neck, lung, breast, colorectal, and prostate) may help doctors predict how patients will respond to treatment with radiation therapy. PURPOSE: This research study is measuring levels of TGF-beta in patients with epithelial cancers who are undergoing radiation therapy.