Endocrine Therapy Base on 21-gene RS

Inclusion criteria

• Histologically confirmed breast cancer.
• Age ≤50 years at initial diagnosis.
• Premenopausal at diagnosis, defined as any of the following:

A. History of menstruation within 6 months prior to diagnosis. B. Serum FSH < 30 mIU/mL. C. If criteria A or B are unavailable, women aged ≤50 years are considered premenopausal.

• Underwent curative-intent breast cancer surgery between January 2012 and December 2021.
• Pathologic tumor stage pT1-pT3 after surgery.
• Pathologic nodal stage pN0-pN1 after surgery.
• Hormone receptor-positive disease by immunohistochemistry (IHC): estrogen receptor (ER) and/or progesterone receptor (PR) positive (≥1% positive cells or Allred score ≥3).
• HER2-negative disease per ASCO/CAP guidelines: IHC 0 or 1+; if IHC 2+, in situ hybridization (FISH or SISH) negative.
• Oncotype DX® performed, meeting one of the following Recurrence Score (RS) ranges:

A. pN0: RS 11-25. B. pN1: RS ≤25.

Exclusion criteria

• Evidence of distant (systemic) metastasis at diagnosis.
• Postmenopausal status at diagnosis, defined as any of the following:

A. Prior bilateral oophorectomy before the breast cancer diagnosis (considered postmenopausal).

B. Prior unilateral oophorectomy alone is not considered postmenopausal (classified as premenopausal).

C. Bilateral oophorectomy performed after breast cancer surgery for therapeutic purposes is not an exclusion; such patients will be categorized as having received ovarian function suppression (OFS).

D. Serum FSH ≥ 30 mIU/mL.

• Hormone receptor-negative or HER2-positive disease.
• Insufficient or unclear data regarding the type of adjuvant therapy received.
• History of another malignancy treated before the breast cancer diagnosis, except for thyroid cancer and non-melanoma skin cancer.
• Bilateral breast cancer.
• Receipt of neoadjuvant systemic therapy prior to surgery.