Abstract PS1-03-11: Relationship between the Incidence of Osteonecrosis of the Jaw due to Bone-Modifying Drugs Administered for Bone Metastases of Breast Cancer, Risk Factors, and Overall Survival

Background: Bone-modifying agents (BMAs), such as zoledronic acid and denosumab, are standard treatments for reducing skeletal-related events in breast cancer patients with bone metastases. Medication-related osteonecrosis of the jaw (MRONJ) is a well-recognized adverse event, particularly after prolonged treatment. Despite this risk, little data exist on the long-term incidence and prognostic implications in real-world practice. Methods: We retrospectively reviewed breast cancer patients with bone metastases who received BMAs for ≥3 months between January 2015 and December 2024 at our institution. Patients who received radiotherapy to the oral cavity or jaw were excluded from the study. Data were collected from the electronic medical records. MRONJ was diagnosed according to established clinical criteria. Overall survival (OS) was compared between patients with and without MRONJ using the Kaplan-Meier method. Results: A total of 46 female patients (median age, 58 years; range, 35-90 years) were included. Thirty-six patients (78.2%) underwent dental assessment before BMA initiation, and 19 (41.3%) underwent tooth extraction. The median treatment duration was 33 months (range 6-85). MRONJ occurred in 16 patients (34.8%) with a median onset time of 23.5 months. Six cases were triggered by tooth extraction during the treatment. Fourteen patients were managed conservatively, and two required surgical debridement.The median OS was significantly longer in the MRONJ group (2048 vs. 1092 days; p = 0.0332), with no difference in BMA duration between the groups. Discussion and Conclusion: Our cohort showed a high incidence of MRONJ, which is consistent with previous long-term data. Notably, MRONJ was associated with a longer OS. Although its causality remains unclear, MRONJ may reflect prolonged disease control or more intensive care. These findings support the continued use of BMAs with proper dental monitoring and aggressive management of MRONJ. Prospective studies are warranted to explore prognostic implications and optimize supportive care strategies.These findings highlight a rare but clinically significant adverse event associated with prolonged use of BMAs in patients with breast cancer. Although the sample size was limited, the long-term follow-up and detailed analysis of dental intervention strategies provided valuable insights for real-world clinical management.As this analysis was conducted exclusively in an Asian population, the findings may offer unique insights into MRONJ risk and outcomes in non-Western breast cancer cohorts, where data remain limited. Citation Format: A. Murakami, M. Manae, U. Kaho, T. Kana, N. Megumi, K. Erina, N. Haruna, T. Kana, K. Yoshiaki, U. Yuzo. Relationship between the Incidence of Osteonecrosis of the Jaw due to Bone-Modifying Drugs Administered for Bone Metastases of Breast Cancer, Risk Factors, and Overall Survival [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 PS1-03-11.