This study investigates if taking a break from endocrine therapy to allow pregnancy affects the risk of breast cancer coming back. It focuses on young women who have had early breast cancer and are interested in becoming pregnant. Endocrine therapy involves using medicines that block certain hormones to slow or stop the growth of cancer. The study will also look at different factors related to fertility, pregnancy, and breast cancer biology.

Participants in the study will have their endocrine therapy temporarily stopped to permit pregnancy. The study will monitor various health indicators related to fertility and breast cancer. Participants will not receive any payment for their involvement in the study.

• Who can participate: Women on endocrine therapy for early breast cancer for 18 to 30 months who wish to become pregnant can participate. Those who have used reproductive technologies or preserved reproductive tissues are also eligible.
• Study details: Participants will stop their endocrine therapy to try and become pregnant. The study will observe fertility and health indicators. There is no payment for participation.