Prospective Cohort Study of Adding Ovarian Function Suppression to Tamoxifen in Young Women With Hormone-sensitive Breast Cancer Who Remain Premenopausal or Resume Menstruation After Chemotherapy

To evaluate the long-term outcomes beyond 10 years of the Korean Breast Cancer Society-sponsored multicenter prospective ASTRRA trial, we aim to compare the effects of adding 2 years of ovarian function suppression (OFS) therapy to standard tamoxifen treatment in premenopausal young women with hormone receptor-positive breast cancer who preserved or recovered ovarian function after chemotherapy. Given the characteristic pattern of delayed recurrence in hormone receptor-positive breast cancer compared with other molecular subtypes, this long-term follow-up study will assess the durability and safety of the treatment strategy by evaluating disease-free survival (DFS) beyond 10 years, breast cancer-specific survival, and overall survival. In addition, through analyses of recurrence patterns according to treatment groups, we aim to determine the long-term impact of additional OFS therapy on reducing different types of recurrence.

Inclusion criteria

• Premenopausal women with hormone receptor-positive breast cancer enrolled in the ASTRRA trial (NCT00912548).

Patients enrolled and randomized in the ASTRRA study between March 1, 2009, and July 17, 2018 (excluding screening failures).

Patients with available long-term follow-up information.

Exclusion criteria

• Patients with primary breast cancer meeting any of the following criteria:

Hormone receptor-negative breast cancer Unknown hormone receptor status

Patients with a history of hysterectomy or bilateral oophorectomy

Patients with breast sarcoma or squamous cell carcinoma of the breast

Patients with a history of malignancy other than breast cancer within 5 years prior to enrollment

Patients with thrombocytopenia

Patients who had previously received CMF chemotherapy (cyclophosphamide, methotrexate, and fluorouracil)