Paricalcitol, Fluorouracil, and Radiation Therapy in Treating Patients With Rectal Cancer That Can Be Removed in Surgery

Inclusion Criteria: Patients must have histologically confirmed T3-T4 adenocarcinoma of rectal mucosal origin or node positive, with no confirmed distant metastases, and that has been shown to be resectable Eastern Cooperative Oncology Group (ECOG) performance status 0-2 Leukocytes \>= 3,000/mcL Absolute neutrophil count \>= 1,500/mcL Platelets \>= 100,000/mcL Total bilirubin within normal institutional limits Aspartate aminotransferase (AST) (serum glutamic oxaloacetic transaminase \[SGOT\])/alanine aminotransferase (ALT) (serum glutamic pyruvate transaminase \[SGPT\]) =\< 2.5 X institutional upper limit of normal Creatinine within normal institutional limits OR creatinine clearance \>= 60 mL/min/1.73 m\^2 for patients with creatinine levels above institutional normal Patients must not have deficient levels of Vitamin D, 1, 25 Hydroxy as defined by the institution (this allows patients with normal vitamin D or insufficient vitamin D) Ability to understand and the willingness to sign a written informed consent document Exclusion Criteria: No prior pelvic radiation therapy or chemo-radiation to the rectum; no chemo-radiation for any other reason in the last 8 weeks Patients may not be receiving any other investigational agents Patients with a history of or current hypercalcemia may not be enrolled in this study History of allergic reactions attributed to compounds of similar chemical or biologic composition to paricalcitol Uncontrolled intercurrent illness including, but no…