Pilot Trial of Supplemental 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.