Predictors of Tumor Response and of Radiation Therapy Side Effects in Patients With Gastrointestinal Cancers

Background: * Gastrointestinal (GI) carcinomas represent one of the most commonly diagnosed malignancies in the United States. * A sensitive and specific marker of tumor persistence or recurrence would permit a more accurate determination of the appropriateness of adjuvant therapy in patients with no clinical evidence of disease following curative resection and allow the diagnosis of recurrences at earlier stages that may be amenable to curative salvage therapies. * A biomarker detectable shortly after treatment or in the early stages of chronic radiation toxicity may allow the identification of patients at risk and early intervention. Objectives: * Our primary objective is to determine if patient specific tumor markers in stool, urine, or serum can be reliably detected prior to treatment and followed after treatment to monitor the extent of residual disease. * A second objective is to evaluate the predictive value of potential markers of chronic gastrointestinal injury after radiotherapy. Eligibility: * Age greater than or equal to 18 years * Histologically confirmed carcinoma of the gastrointestinal tract (esophagus, stomach, pancreas, rectum) * Planned to receive radiotherapy to the site of the gastrointestinal malignancy on an National Cancer Institute (NCI) protocol Design: * This protocol provides a means of acquiring tissue, serum, urine, and stool samples from patients who will receive radiation therapy as part of their treatment for gastrointestinal malignancies. * Patients treated with radiation therapy on NCI treatment protocols will be asked to provide samples prior to any local or systemic therapy as well as before, during and after their radiation treatment. * These samples will be tested for the presence of tumor specific deoxyribonucleic acid (DNA) mutations and aberrant methylation patterns determined to be present in each patient's tumor by screening of initial biopsy or surgical material. * Tumor markers specific to each patient, such as tumor specific DNA mutations or aberrant DNA methylation, may provide an individualized method to evaluate disease status and determine prognosis after therapy. Additionally, a number of stool and serum markers will be explored as early indicators of acute and eventual chronic gastrointestinal injury in patients receiving radiotherapy to the abdomen.