The goal of this clinical trial is to assess the feasibility and safety of oral nicotinamide (NAM; a derivative of vitamin B3 [niacin]) and vitamin A in a high-risk population of kidney transplant recipients with a history of skin cancer to generate preliminary data for future cancer prevention clinical trials.

Inclusion Criteria:

• 18 years old or greater;
• Either History of 2 or more histologically confirmed invasive cutaneous SCCs in the past 2 years or
• At least one previously billed Healthcare Common Procedure Coding System code 17004 (destruction of 15 or more benign or premalignant lesions of the integumentary system);
• Understands, reads, and writes English proficiently.

Exclusion Criteria:

• Liver disease;
• Active peptic ulcer disease;
• Recent myocardial infarction;
• Hypotension;
• Internal malignancy within past 5 years;
• Renal impairment with eGFR<15 mL/min/1.73 m2;
• Being unable for follow up due to social reasons;
• Gorlin's syndrome or other genetic skin cancer syndrome;
• Huge number of current skin cancers;
• Metastatic SCC or invasive melanoma within the past 5 years;
• Pregnancy or lactation;
• Need for ongoing carbamazepine use (which could have a possible interaction with NAM);
• Use of acitretin or other oral retinoids within the past 6 months;
• Use of supplemental NAM, niacin, vitamin A, or beta carotene within the past 6 months;
• Field treatment for actinic keratoses (AKs) within the previous 4 weeks;
• Use of topical steroids.