Effects of Nicotinamide in Patients With Chronic Lymphocytic Leukemia With History of Non-melanoma Skin Cancers

Inclusion Criteria: * Male or female subject aged ≥ 18 years. * Confirmed diagnosis of CLL or small lymphocytic leukemia (SLL) per iwCLL 2018 criteria. * History of ≥1 non-melanoma skin cancer (NMSC) diagnosed within the last 5 years * Adequate liver function as defined as: * Total Bilirubin ≤ 1.5x institutional upper limit of normal (ULN) ---Subjects with a known diagnosis of Gilbert's Syndrome: direct bilirubin ≤ 1.5x ULN * AST(SGOT)/ALT(SGPT) ≤ 3 × institutional ULN * For female subjects: Negative pregnancy test or evidence of post-menopausal status. The post-menopausal status will be defined as having been amenorrheic for 12 months without an alternative medical cause. The following age-specific requirements apply: --Women \< 50 years of age: * Amenorrheic for ≥ 12 months following cessation of exogenous hormonal treatments; and * Luteinizing hormone and follicle-stimulating hormone levels in the post-menopausal range for the institution; or * Underwent surgical sterilization (bilateral oophorectomy or hysterectomy). * Women ≥ 50 years of age: * Amenorrheic for 12 months or more following cessation of all exogenous hormonal treatments; or * Had radiation-induced menopause with last menses \>1 year ago; or * Had chemotherapy-induced menopause with last menses \>1 year ago; or * Underwent surgical sterilization (bilateral oophorectomy, bilateral salpingectomy, or hysterectomy). * Female subjects of childbearing potential and male subjects with a sexual partner of childbearing potential must agree to use a highly effective method of contraception. Exclusion Criteria: * Received cytotoxic chemotherapy (including fludarabine, cyclophosphamide, bendamustine, or chlorambucil) within the last 6 months * Received allogeneic stem cell transplant within the last 6 months. * Taking nicotinamide or niacin supplements within the last 4 weeks. * Taken acitretin or other oral retinoids within the past 6 months * Received field treatment for AKs (topical use of 5-fluorouracil, imiquimod, diclofenac, retinoids; topical photodynamic therapy for AKs; laser resurfacing or chemical peel treatments for AKs) within the previous 4 weeks * Large areas of confluent skin cancer at baseline preventing accurate assessment and counting of individual new skin cancers * Need for ongoing carbamazepine use (possible interaction with nicotinamide) * Severe GI malabsorption that may interfere with absorption of nicotinamide (per investigator's discretion) * Patients with an expected life expectancy \< 2 years * Current evidence of uncontrolled, diabetes. * Current evidence or history of peptic ulcer disease. * Known HIV infection with a detectable viral load within 6 months of the anticipated start of treatment. Note: Subjects on effective antiretroviral therapy with an undetectable viral load within 6 months of the anticipated start of treatment are eligible for this trial. * Known active uncontrolled infection. * Medical, psychiatric, cognitive, or other conditions that may compromise the subject's ability to understand the subject information, give informed consent, comply with the study protocol or complete the study. * Known prior severe hypersensitivity to investigational product (IP) or any component in its formulations (NCI CTCAE v5.0 Grade ≥ 3). * Subjects taking prohibited medications as described in study protocol. A washout period of prohibited medications for a period of at least five half-lives or as clinically indicated should occur before the start of treatment. * Have ever received a solid organ transplant and are currently taking immunosuppressive medications.