Pilot Trial of Supplemental Vitamin A and Nicotinamide and Levels of Blood Vitamin A and Nicotinamide

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.