Blood Test to Predict Radiation Response and Toxicity in Patients Undergoing Radiation Therapy

Inclusion Criteria: 1. Male and female patients age 18 or older 2. Diagnosed with a primary rectal or esophageal cancer 3. Planned radiation therapy to the esophagogastric area to a minimum of 4140 cGy for esophageal/gastroesophageal junction cancer or to pelvis to a minimum of 4500 cGy for rectal cancer as part of clinical care 4. Combining chemotherapy is allowed 5. ECOG Performance Status 0-2 6. Able to provide written informed consent Exclusion Criteria: 1. Subjects who have received radiation within three (3) months to esophagogastric or pelvic areas prior to consent 2. Subjects, who in the opinion of the investigator, may not be able to comply with the requirements of the study