5-Fluorouracil and Calcipotriene for Treatment of Low Grade Skin Cancer

Inclusion Criteria: * English-speaking * Having a previously untreated, biopsy-proven Superficial Basal Cell Carcinoma (sBCC) or Squamous Cell Carcinoma in Situ (SCCis) of the skin \<2 cm on the scalp, trunk, neck, or extremities, excluding hands, feet, and genitalia * Having a previously untreated, biopsy-proven sBCC or SCCis on the face, hands, feet, and genitalia who decline surgery or are otherwise not surgical candidates * Willing to undergo all protocol requirements and attend study-specific follow up clinic visits in addition to routine follow up visits * Participants may have multiple lesions enrolled in the study so long as the individual lesions are greater than 2 cm from each other * If a woman is of childbearing potential, the participant must be willing to take a pregnancy test before starting treatment and be on some form of birth control while receiving treatment. Birth control can include abstinence, oral contraceptive pill, intrauterine device, implanted birth control device, birth control patch, or the vaginal ring. The patient does not need to be on any form of birth control after they end therapy. Exclusion Criteria: * Current or prior field treatment within 2 cm of the target BCC or SCCis * Periorbital lesions * Lesions that have been previously treated * Known allergy to any of the study medication ingredients * History of solid organ transplant or current immunosuppression * Genetic disorders associated with high skin cancer risk * Arsenic exposure * Cutaneous T-cell lymphoma * Current or prior radiation therapy at the site of the sBCC or SCCis * Women who are pregnant or currently breastfeeding * Prior psoralen plus Ultraviolet light (UVA) treatment at the site * Very high mortality risk at the start of the study * Dihydropyrimidine dehydrogenase (DPD) enzyme deficiency * Demonstrated hypercalcemia or evidence of vitamin D toxicity * Lesions that extend into the oral, nasal or genital mucosa