Lower-Dose Chemoradiation in Treating Patients With Early-Stage Anal Cancer, the DECREASE Study

Inclusion Criteria: * STEP 0 (PRE-REGISTRATION) * Patient must be ≥ 18 years of age * Patients must be English speaking to participate in the trial. (Please note that this requirement is due to the fact that the quality-of-life studies are mandatory and we currently do not have full translated versions of the questionnaires into other languages) * Patient must have histologically proven T1-2N0M0 invasive anal canal or anal margin squamous cell carcinoma with tumors measuring =\< 4 cm. This may include tumors of non-keratinizing histology such as basaloid, transitional cell or cloacogenic histology. Measurable disease is not required * Patients who are status/post local excision or excisional biopsy procedure are eligible provided there was tumor involvement of the anal canal and/or anal verge prior to the reaction, if the margins were positive, and/or if the stage is T2N0 based on tumor size before the procedure. This means that patients with T1N0M0 anal margin squamous cell carcinoma who underwent surgical excision with negative margins and no involvement of the anal verge and/or anal canal are not eligible * Tumor size must be documented based on physical examination including digital rectal exam and/or anoscopy/proctoscopy within 4 weeks prior to Step 0 pre-registration * Patient's human immunodeficiency virus (HIV) status must be known and documented at baseline * NOTE: For patients without a history of HIV infection, it is recommended (but not required) that updated …