Phase I Trial of Endoxifen Gel Versus Placebo in Women Undergoing Breast Surgery

Inclusion Criteria: * Women scheduled for unilateral or bilateral mastectomy for breast cancer therapy, pathology confirmed stage 0-III (including ductal carcinoma in situ), or prophylaxis (BRCA1/2 mutation carriers, women with strong family history or lobular carcinoma in situ or other conditions where prophylactic mastectomy has been elected) * Age \>= 18 years (since breast cancer is not a pediatric disease and no safety data are available for ENX use in children) * Eastern Cooperative Oncology Group (ECOG) performance status =\< 1 (Karnofsky \>= 70%) * Total bilirubin \< 1.5 x upper limit of normal (ULN) (in women with prior documented bilirubin elevations consistent with Gilbert's syndrome, total bilirubin up to 3 x ULN will be allowed) * Aspartate aminotransferase (AST) (serum glutamic-oxaloacetic transaminase \[SGOT\]) \< 2.5 x ULN * Alanine aminotransferase (ALT) (serum glutamate pyruvate transaminase \[SGPT\]) \< 2.5 x ULN * Creatinine \< 2 x ULN * Alkaline phosphatase \< 2.5 x ULN * Blood urea nitrogen \< 2 x ULN * Ability to understand and the willingness to sign a written informed consent document which includes a requirement to apply study agent to sensitive body parts daily * Willingness and ability to schedule mastectomy 21-28 days following start of study agent; women with breast implants may participate * Willingness to avoid exposing breast skin to natural or artificial sunlight (i.e. tanning beds) for the duration of study agent dosing * Negative urine or …