<qa>  What is the dose level associated with endoxifen steady state concentration?l. To determine either the maximum-tolerated dose MTD of Z-endoxifen hydrochloride or the dose level associated with endoxifen steady state concentration Css of at least 2 uM in women with metastatic estrogen-receptor positive ER breast cancer. Dose Escalation Cohort II. To describe the safety profile of Z-endoxifen Z-endoxifen hydrochloride at each of the doses examined. Dose Escalation Cohort III. To evaluate changes in vision after 2 cycles of treatment. Dose Escalation Cohort IV. To gather preliminary data on the clinical benefit in terms of tumor response rate and progression-free survival. Dose Escalation Cohort V. To evaluate the changes in the frequency and severity of hot flashes after 2 cycles of treatment. Expansion Cohort VI. Evaluate changes in irritability scale using a validated irritability questionnaire. Expansion Cohort VII. To evaluate changes in markers of bone formation and absorption after 2 cycles of treatment. Expansion Cohort XIII. To evaluate changes in vision after 2 cycles of treatment. Expansion Cohort. 