Afimoxifene in Reducing the Risk of Breast Cancer in Women With Mammographically Dense Breast

Inclusion Criteria:

Women age 40-69 years, or less than 40 years if 5-year breast cancer Gail risk is ≥ 1.66%.
Mammographically dense breast (heterogeneously dense [C] or extremely dense [D], based on American College of Radiology [ACR] BIRADS fifth edition classification or heterogeneously dense [3] or extremely dense [4], based on ACR BIRADS fourth edition classification) in either breast
Eastern Cooperative Oncology Group (ECOG) performance status =< 1 (Karnofsky >= 70%)
White blood cells >= 3,000/microliter
Absolute neutrophil count >= 1,500/microliter
Platelets >= 100,000/microliter
Total bilirubin within normal institutional limits
Aspartate aminotransferase (AST) (serum glutamic-oxaloacetic transaminase [SGOT])/alanine aminotransferase (ALT) (serum glutamate pyruvate transaminase [SGPT]) =< 1.5 × institutional upper limit of normal (ULN)
Creatinine within normal institutional limits
Participant must have a gynecology examination within the last 3 years, with no atypical hyperplasia and no cancer
Premenopausal women taking non hormonal intra-uterine device (IUD) birth control method will be eligible, if they have been on the same IUD for at least 3 months prior to enrollment and plan to continue using the same method throughout the study
Women of child-bearing potential must agree to use a reliable nonhormonal contraceptive method during the study and for 2 months after completing study medications; reliable nonhormonal methods of contraception include barrier contraception and an intra-uterine device (IUD); Note: women who had tubal ligation or had a partner who had undergone a vasectomy (and are monogamous) are eligible for the study and are not required to use barrier contraception
If the participant is of childbearing potential, she must have a documented negative urine pregnancy test within 7 days prior to randomization
Willingness to avoid exposing breast skin to natural or artificial sunlight (i.e. tanning beds) for the duration of the study
Ability to understand and the willingness to sign a written informed consent document

Exclusion Criteria:

History of allergic reactions attributed to compounds of similar chemical or biologic composition to 4-OHT gel
Uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, thromboembolic disease, or psychiatric illness/social situations that would limit compliance with study requirements
Pregnant, or had given birth, or nursed at any time during the last 12 months
Women with a previous history of invasive breast cancer or bilateral ductal carcinoma in situ (DCIS) or current untreated DCIS; women with a history of cancer within the last 3 years, except for non-melanoma skin cancer; women with unilateral DCIS (with or without radiation therapy) are eligible as long as they have an unaffected breast
Prior bilateral breast surgery (mastectomy, segmental mastectomy, or breast augmentation surgery including breast implants or breast reductions)
Women with "mosaic mammographic screening views", i.e., whose larger breast size precludes being imaged within a single mammographic screening view
Women with active liver disease, abnormal uterine bleeding, or prior diagnosis of endometrial hyperplasia
Prior use of selective estrogen receptor modulators (SERMS) and aromatase inhibitors (AIs) for prevention or therapy
Skin lesions on the breast that disrupt the stratum corneum (e.g., eczema, ulceration)
Treatment with any investigational drug or investigational biologic within 30 days of initiating study treatment or during the study