Table 1.

Recommended Adjuvant Therapy for Women with ER+ HER2- Breast Cancer.

Drug Class	Medication	Dose/Administration	Mechanism of Action
SERM	Tamoxifen [17]	20 mg PO once daily	Inhibitory effect on estrogen-regulated pathways through competitive mechanisms of ER-binding, leading to suppression of mammary tumor angiogenesis
AI Non-Steroidal Steroidal	Anastrozole [18] Letrozole [19] Exemestane [20]	1 mg PO once daily 2.5 mg PO once daily 25 mg PO once daily	By inhibiting the aromatase enzyme, it reduces the circulating estrogen levels by suppressing its conversion from androgens, predominantly in adipose tissues
GnRHa	Goserelin [21] Leuprolide [22] Triptorelin [23]	3.6 mg SubQ q28 days 3.75 mg IM q28 days 3.75 mg IM q28 days	Chemical castration leading to lower secretion of FSH and LH, thereby suppressing estrogen levels
CDK 4/6 Inhibitor	Abemaciclib [24]	150 mg PO twice daily	Selective inhibition of CDK4 and CDK6, subsequently terminating the cell cycle at the G1 phase by interrupting pRb phosphorylation
Bisphosphonate *	Zoledronic Acid [25] Clodronate [26] Ibandronate [27]	4 mg IV q6 month 1600 mg PO daily 50 mg PO daily	Inhibits osteoclasts by way of apoptosis, and thereby decreases bone resorption and increases bone mineralization

* Dosing, mode of administration and total duration of the bisphosphonates recommended by ASCO guideline [28]: Zoledronic Acid 4 mg IV every 6 months for 3 years or at 4 mg once every 3 months for 2 years. Clodronate 1600 mg PO daily for 2 to 3 years. Ibandronate 50 mg PO daily for 3 years. SERM: Selective Estrogen Receptor Modulator, ER: Estrogen Receptor, PO: Per oral, AI: Aromatase Inhibitor, IV: Intravenous, SubQ: Subcutaneous, IM: Intramuscular, GnRHa: Gonadotropin-releasing hormone agonist, FSH: Follicle stimulating hormone, LH: Luteinizing hormone, CDK 4/6: Cyclin-Dependent Kinase 4/6 inhibitor, pRb: Retinoblastoma protein.