A Study to Evaluate the Effect of Vitamin D on PFS in Indolent Non-Hodgkin's Lymphoma

Inclusion Criteria

• Inclusion Criteria: Each of the following criteria must be met in order for a patient to be considered eligible for registration: - Biopsy proven (with hematopathology review at one of the participating sites to confirm correct histology in accordance with World Health Organization) indolent lymphoma to include the following diagnoses: - Grade 1, 2, or 3a follicular lymphoma - Small lymphocytic lymphoma (CLL excluded) - Marginal zone lymphoma (nodal or splenic) - Mucosal-associated lymphoid tissue - Measurable disease defined by Lugano criteria - No prior anti-lymphoma systemic therapy; prior radiation therapy allowed - Age 18 or over - Ann Arbor stages II, III or IV - Patients with follicular lymphoma must have PET FDG-avid lymphoma and fulfill Low tumor burden by Groupe D'Etude des Lymphomes Folliculaires (GELF) criteria: - No mass > 7 cm - < 3 distinct masses of greater than 3 cm - No B symptoms - No splenomegaly > 16 cm by computed tomography (CT) scan - No risk of vital organ compression - No leukemic phase > 5000/µl circulating lymphocytes (except for in patients with splenic marginal zone diagnosis) - No cytopenias (platelets < 100,000/µl, hemoglobin < 10 g/dl, or absolute neutrophil count < 1500/µl) Exclusion Criteria: The following criteria will prevent inclusion of an inappropriate subject into the trial: - Osteoporosis requiring prescription treatment - Known symptomatic primary hyperparathyroidism - Hypercalcemia defined as above the institutional normal range (corrected for albumin when albumin levels are below normal) - History of calcium-related kidney stones - Creatinine > 1.5X above upper limit of normal - Women who are known to be pregnant or who plan to become pregnant while on rituximab treatment