Abstract PS2-02-15: The impact of ASCO/CCO guidelines on the use of adjuvant bone-modifying agents by specialized and general oncologists for elderly patients with breast cancer

Abstract Background: In 2017, the American Society of Clinical Oncology (ASCO) and Cancer Care Ontario (CCO) jointly published guidelines recommending discussion of adjuvant bisphosphonate therapy for all postmenopausal patients with early-stage breast cancer deemed candidates for systemic therapy. We evaluated the impact of this guideline on the use of adjuvant bone-modifying agents (BMAs) among patients in SEER-Medicare to understand if 1) the guidelines were effective in changing prescribing patterns and 2) there was a difference in the effect of the guidelines on specialized vs generalist oncologists. Methods: We identified women aged 65-85 years with localized or regional breast cancer diagnosed between 2012 and 2018 and continuously enrolled in Medicare fee-for-service for at least 1 year after diagnosis. We excluded patients with missing hormone receptor (HR) or HER2 status, no claims for surgery, radiation, or systemic therapy after diagnosis, death within 6 months of diagnosis, BMA use before breast cancer diagnosis, and those without an identifiable primary oncologist. Primary endpoints were: 1) use of a BMA within 1 year of diagnosis and 2) choice of bisphosphonate vs denosumab. We used multivariate logistic regression to examine the correlation of key factors (age, comorbidity, race/ethnicity, the treating oncologist’s degree of breast cancer specialization) with each endpoint. We report odds ratios (OR) and 95% confidence intervals (CI) from the multivariate analyses. We defined an oncologist’s breast cancer specialization as the percentage of patients with breast cancer they treated, relative to the total SEER-Medicare patients with colon, lung, or breast cancer. We designate oncologists with the highest quartile of breast cancer cases as “specialized” and the other 75% as “generalists”. Results: The cohort included N=76,498 patients. BMA use increased in HR+ disease from 7.4% (95% CI 6.8-8.0%) in 2012 to 12.1% (11.5-12.7%) in 2018, while there was no change in usage in HR- disease (2.2% [1.3-3.1%] in 2012 and 2.2% [1.4-3.0%] in 2018). Specialized oncologists used less BMA overall than generalist oncologists (OR 0.84 [0.80-0.89]). This difference was driven by lower BMA use by specialists in localized HR+ disease (OR 0.79 [0.74–0.84]), with no significant difference in regional or HR- disease (OR 0.97 [0.88–1.08]). There was no clear effect of the guideline publication on the temporal trend of overall BMA use. However, we observed an increase in the selection of bisphosphonate over denosumab after the guideline publication, with the proportion using bisphosphonate increasing from 21.5% (19.8-23.3%) (2015-2016) to 36.1% (34.2-38.0%) (2017-2018). This shift post-guideline was more pronounced in the specialized oncologists (p for interaction = 0.003); the proportion using bisphosphonate (vs denosumab) increased from 20.7% (17.9-23.6%) to 40.7% (37.5-43.8%) in specialized oncologists, compared to an increase from 22.0% (19.8-24.1%) to 33.4% (31.1-35.7%) in generalist oncologists. Overall, BMA use was higher for HR+ vs HR- disease (OR 4.40 [3.82-5.07]), regional vs localized stage (OR 1.17 [1.10-1.24]), older vs younger patients (OR 1.10 [1.04-1.16] for 75-85 vs 65-74), and Asian vs White patients (OR 1.38 [1.23-1.55]), and lower for Black vs White patients (OR 0.63 [0.55-0.71]). Conclusions: Specialized oncologists used adjuvant BMAs less frequently in patients with lower-risk HR+ disease compared to generalist oncologists. They were also more sensitive to the guideline release, demonstrating greater uptake of the recommendation for bisphosphonate over denosumab. Broader alignment with specialist prescribing patterns could promote more efficient resource utilization across the Medicare population. Citation Format: N. Dalal, H. Tang, M. Reitsma, J. Dickerson, S. Phillips, B. Staiger, J. Goldhaber-Fiebert, J. Caswell-Jin. The impact of ASCO/CCO guidelines on the use of adjuvant bone-modifying agents by specialized and general oncologists for elderly patients with breast cancer [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS2-02-15.