Inclusion Criteria:  Male or female subject aged ≥ 18 years. Histologically confirmed diagnosis of CLL per iwCLL 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 as described in Section 5.4.1.  Exclusion Criteria:  Received chemotherapy (such as 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.  - Active infection including tuberculosis (clinical evaluation that includes clinical history, physical examination, radiographic findings, and TB testing in line with local practice), or hepatitis C.  Note: Subjects positive for hepatitis C (HCV) antibody are eligible only if polymerase chain reaction is negative for HCV RNA.  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 Section 6.7.1. 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.