I. To establish the dermal tolerability and safety of Z-endoxifen hydrochloride (endoxifen) (ENX) gel administered topically to both breasts at two doses: 10 mg daily (5 mg per breast) and 20 mg daily (10 mg per breast) in comparison to vehicle placebo gel, using objective assessments based on Common Terminology Criteria for Adverse Events (CTCAE) criteria.