Pregnancy Outcome and Safety of Interrupting Therapy for Women With Endocrine Responsive Breast Cancer

Inclusion Criteria: * Age ≥ 18 and ≤ 42 years at enrollment. * Has received adjuvant endocrine therapy (SERM alone, GnRH analogue plus SERM or AI) for ≥18 months but ≤30 months for early breast cancer. Note: Patients who have received neo/adjuvant endocrine treatment within a clinical trial and patients who have received pharmaco-prevention are eligible. * The adjuvant endocrine therapy must have stopped within 1 month prior to enrollment. * Patient wishes to become pregnant. Note: Patients who have undergone oocyte/embryo/ovarian tissue cryopreservation at breast cancer diagnosis and/or have a previous history of assisted reproductive technology (ART) are eligible. * Breast cancer for which patient is receiving endocrine therapy must have been histologically-proven stage I-III, endocrine-responsive (i.e., estrogen and/or progesterone receptor positive, according to local definition of positive, determined using immunohistochemistry (IHC)), and treated with curative intent. Note: * Patients with synchronous bilateral invasive breast cancer (diagnosed histologically within 2 months) are eligible. * Patient with invasive breast cancer or synchronous bilateral invasive breast cancer (diagnosed histologically within 2 months) during pregnancy are eligible. * Patients with BRCA1/2 mutations are eligible. * Patients could have received neo/adjuvant chemotherapy, or other systemic therapy (e.g., neo/adjuvant HER2-targeted therapy) according to institutional policy and patient's…