Cholecalciferol and Calcium Carbonate in Treating Patients With Colon Cancer That Has Been Removed by Surgery

OBJECTIVES: Primary * Compare the antiproliferative effects of 2 different doses of cholecalciferol (i.e., vitamin D3) in combination with calcium carbonate on the proliferative labeling index in patients with resected colon cancer. Secondary * Compare the effects of these doses on serum levels of 25-OH-D3, 1,25-OH-D3, 24,25-OH-D3, calcium, and parathyroid hormone in these patients. * Determine the safety of high-dose cholecalciferol in these patients over 2 years. * Compare the effects of these doses on several biological markers (i.e., cyclin D1, protein kinase C, vitamin D receptor, p21, and p27) in the rectal mucosa of these patients. OUTLINE: This is a randomized, pilot study. Patients are randomized to 1 of 2 treatment arms. * Arm I: Patients receive oral low-dose cholecalciferol once daily and oral calcium carbonate twice daily. * Arm II: Patients receive oral high-dose cholecalciferol once daily and calcium carbonate as in arm I. Treatment in both arms continues for up to 2 years in the absence of disease progression or unacceptable toxicity. All patients undergo sigmoidoscopy or colonoscopy with 4 quadrant mucosal biopsies at baseline and after 6 months of study treatment. After their 6-month mucosal biopsy, patients in arm I switch to high-dose cholecalciferol as in arm II. Patients undergo blood, urine, and tissue collection periodically during study for pharmacokinetic, pharmacodynamic, and/or histopathological analysis. Serum is collected monthly for 3 months and then once every 3 months to assess changes in serum levels of vitamin D and vitamin D metabolites (i.e., 1,25-OH-D3; 25-OH-D3; 24,25-OH-D3), as well as changes in calcium and parathyroid hormone, BUN, creatinine, electrolytes, and phosphorus levels. Urine is collected once every 3 months to assess changes in urine calcium and creatinine levels for hypercalciuria. Tissue biopsies of normal endorectal mucosa collected at baseline and after 6 months of study treatment are evaluated by IHC for proliferative index, vitamin D receptor staining, p21, p27, cyclin D1, and protein kinase C. PROJECTED ACCRUAL: A total of 20 patients will be accrued for this study.