Protecting Bone Health During Breast Cancer Endocrine Therapy

A prescription for an aromatase inhibitor can begin years of treatment after surgery or chemotherapy ends. During that time, estrogen suppression can accelerate bone loss, increasing fracture risk even as endocrine therapy reduces the risk of breast cancer recurrence. Bone protection belongs in the treatment plan from the outset.¹

For pharmacists, the opportunity extends beyond recommending a calcium supplement. Medication reviews can uncover untreated fracture risk, while refill encounters provide opportunities to confirm that patients have received recommended assessments and understand their bone-directed therapy.

Assess Risk Before Bone Loss Progresses

The skeletal effects of endocrine therapy depend on treatment and menopausal status. Aromatase inhibitors increase bone loss in postmenopausal patients; ovarian suppression also warrants attention in younger patients. Tamoxifen generally preserves bone mass after menopause, but its effects differ before menopause.¹

The American Society of Clinical Oncology (ASCO) recommends assessing fracture risk in survivors of nonmetastatic cancer and obtaining bone mineral density testing when risk is substantial. Pharmacists can ask whether a baseline dual-energy x-ray absorptiometry assessment has been completed and flag prior fragility fractures or prolonged corticosteroid exposure for the treating team.²

The 2025 updated joint position statement on aromatase inhibitor–associated bone loss recommends monitoring risk and bone mineral density every 1 to 2 years in patients with a T-score above −2.0 and no additional risk factors. A T-score below −2.0, or at least 2 clinical risk factors, supports starting an antiresorptive under its treatment algorithm.¹

These thresholds differ from general osteoporosis criteria. Pharmacists should confirm which guideline informs the patient’s plan rather than assume treatment must wait until osteoporosis develops.

Make Supportive Measures Specific

ASCO recommends adequate calcium and vitamin D intake, with supplementation when dietary intake is insufficient. Its guideline targets total calcium intake of 1000 to 1200 mg daily and vitamin D intake of at least 800 to 1000 IU daily. Weight-bearing activity and resistance exercise should accompany attention to fall prevention.²

A practical pharmacy review starts with what the patient already takes. Comparing supplement labels with dietary intake helps identify gaps without automatically adding another product. Patients at elevated fracture risk need assessment for pharmacologic protection; supplements alone do not replace indicated treatment.²

Match the Drug to the Treatment Goal

Fracture prevention and recurrence reduction are separate reasons to prescribe bone-modifying therapy. For osteoporosis or elevated fracture risk in nonmetastatic cancer survivors, ASCO identifies bisphosphonates or denosumab (Prolia, Xgeva; Amgen) at osteoporosis-indicated doses as preferred options when medication is needed.²

The randomized ABCSG-18 trial (NCT00556374) provides direct fracture evidence for denosumab. Among 3420 postmenopausal patients receiving aromatase inhibitors for hormone receptor–positive early breast cancer, denosumab 60 mg subcutaneously every 6 months reduced the hazard of a first clinical fracture compared with placebo (HR, 0.50; 95% CI, 0.39–0.65; P < .0001). Investigators reported 92 fractures with denosumab versus 176 with placebo.³

For recurrence prevention, the ASCO–Ontario Health guideline recommends discussing adjuvant bisphosphonates with postmenopausal patients, including those with therapy-induced menopause, who are candidates for adjuvant systemic therapy. Expected benefit depends on recurrence risk and must be weighed against adverse effects and patient preferences. The guideline does not recommend adjuvant denosumab to prevent recurrence because findings have been inconsistent.⁴

Documenting the indication helps pharmacists verify that the regimen matches its intended purpose.

Plan for Safety and Continuity

Before denosumab begins, preexisting hypocalcemia must be corrected. Its prescribing information includes a boxed warning for severe hypocalcemia in advanced chronic kidney disease, particularly when chronic kidney disease–mineral and bone disorder is present. These patients require specialist supervision and close calcium monitoring.⁵

Dental assessment also matters. Denosumab labeling recommends an oral examination before treatment and preventive dentistry for patients with osteonecrosis-of-the-jaw risk factors. Pharmacists can reinforce oral hygiene and encourage communication about planned invasive dental procedures.⁵

Discontinuation requires a plan: multiple vertebral fractures have occurred after denosumab is stopped, and labeling directs transition to another antiresorptive agent. Tracking injection dates and escalating access problems can help prevent an unintended interruption.⁵

At each endocrine therapy refill, pharmacists can reconnect the patient with the bone health plan: confirm the next assessment, address medication concerns, and identify who will manage follow-up. That continuity makes fracture prevention part of everyday breast cancer care.

REFERENCES

1. Hadji P, Aapro M, Al-Dagri N, et al. Management of aromatase inhibitor-associated bone loss (AIBL) in women with hormone-sensitive breast cancer: An updated joint position statement of the IOF, CABS, ECTS, IEG, ESCEO, IMS, and SIOG. J Bone Oncol. 2025;53:100694. doi:10.1016/j.jbo.2025.100694

2. Shapiro CL, Van Poznak C, Lacchetti C, et al. Management of osteoporosis in survivors of adult cancers with nonmetastatic disease: ASCO Clinical Practice Guideline. J Clin Oncol. 2019;37(31):2916-2946. doi:10.1200/JCO.19.01696

3. Gnant M, Pfeiler G, Dubsky PC, et al. Adjuvant denosumab in breast cancer (ABCSG-18): a multicentre, randomised, double-blind, placebo-controlled trial. Lancet. 2015;386(9992):433-443. doi:10.1016/S0140-6736(15)60995-3

4. Eisen A, Somerfield MR, Accordino MK, et al. Use of adjuvant bisphosphonates and other bone-modifying agents in breast cancer: ASCO-OH (CCO) Guideline Update. J Clin Oncol. 2022;40(7):787-800. doi:10.1200/JCO.21.02647

5. Prolia. Prescribing information. Amgen Inc; 2026. Accessed October 23, 2026. https://www.pi.amgen.com/-/media/Project/Amgen/Repository/pi-amgen-com/Prolia/prolia_pi.pdf