Trial of 4-Hydroxytamoxifen (4-OHT) Gel in Women Aimed at Reducing Dense Breast Tissue

Inclusion Criteria: 1. Healthy women age 35 - 75 years with either heterogeneously dense (C) or extremely dense (D), breast tissue on 2D mammography, based on American College of Radiology (ACR) Breast Imaging-Reporting and Data System (BI-RADS©) fifth edition classification) in either breast within 3 months prior to randomization. Mammogram with BI-RADS final assessment category 1 or 2 (negative or benign findings). 2. If the participant is of childbearing potential, she must have a documented negative urine pregnancy test at the time of screening and randomization and no plans to become pregnant for the duration of study participation. 3. Ability to understand and the willingness to sign a written informed consent document. Exclusion Criteria: 1. Participants may not be receiving treatment with any investigational drug or biologic within 30 days of randomization or at any time during the study. 2. Women with a history of allergic reactions attributed to compounds of similar chemical or biologic composition to Tamoxifen. 3. Pregnant women are excluded from this study because the effects of 4-OHT gel on the developing human fetus at the recommended dose and route are unknown. 4. Pregnancy (independent of outcome) and/or lactation within 1 year prior to the screening mammogram. 5. Women with previous history of cancer (including invasive or intra-ductal breast cancer) except for non-melanoma skin cancer. 6. Women who have had a prior mastectomy (unilateral or bilateral), segmental mastectomy, reduction mammoplasty or breast augmentation including implants. 7. Women with surgical breast biopsy(s) performed within 3 years or core biopsy(s) performed within 1 year prior to the screening mammogram. 8. Women with an abnormal mammogram (BI-RADS final assessment category 3-probably benign, 4-suspicious, or 5-malignant findings). Women with BI-RADS 0 assessment (needs additional imaging evaluation) that are subsequently found to have negative (BI-RADS 1) or benign findings (BI-RADS 2), are NOT excluded. 9. Women with only synthetic 2D mammograms generated from 3D (tomosynthesis) are excluded as breast density measurements are not yet validated for synthetic mammograms. Women with combination 2D+3D mammograms are not excluded. 10. Women with active liver disease or thromboembolic disorder. 11. Women with skin conditions such as psoriasis, fungal infections, keloids etc., or tattoos and/or piercings, which in the opinion of the Investigator, would interfere with absorption of the Investigational Product. 12. Women who have had an abnormal gynecology exam within the last three years with clinically significant findings, such as secondary dysmenorrhea, polyps, or atypia, which in the opinion of the Investigator would interfere with the study. 13. Women who have received treatment with Selective Estrogen Receptor Modulators (SERMs) (e.g. tamoxifen, raloxifene) or aromatase inhibitors 14. Women taking estrogen containing contraceptives or Hormone Replacement Therapy (HRT) must discontinue the treatment a minimum of 6 months prior to the screening mammogram. Progestin only contraceptives are permitted. 15. Women with a concurrent illness, disease or condition that, in the opinion of the Investigator, would limit their compliance with study requirements or place them at additional risk.