279P Incidence, risk factors and management of medication-related osteonecrosis of the jaw in breast cancer patients treated with zoledronic acid or denosumab over a 5-year period in a UK tertiary institution

Bone modifying agents (BMAs) such as Zoledronic acid (ZA) and Denosumab (Dmab) are indicated in metastatic breast cancer (MBC) with bone involvement to prevent skeletal-related events.1 In the early breast cancer (EBC) setting, bisphosphonates reduce distant/bone recurrence and breast cancer mortality in post-menopausal women.2 Although well tolerated, BMAs carry a risk of severe adverse events such as medication-related osteonecrosis of the jaw (MRONJ). Our aim was to assess the incidence, risk factors and management of MRONJ in breast cancer patients receiving ZA and Dmab at our centre. All breast cancer patients, who received at least one dose of ZA or Dmab between 2015 and 2020, were retrospectively identified using Chemocare v6. Electronic records were reviewed till 15/01/2024 for ONJ incidence. Clinical details were collated using Microsoft Excel. SPSS v29.0.2 was utilised for statistical analysis. 455 patients received at least 1 dose of ZA or Dmab. 102 (22.4%) and 353 (77.6%) had diagnoses of EBC and MBC respectively (Table). 17 (3.7%) patients developed MRONJ. Majority were MBC patients receiving palliative monthly Dmab; 1 patient had switched from Dmab to ZA. Mean duration of BMA treatment was 2.2 years (10 months – 4 years). Concurrent systemic treatments included chemotherapy, 3 (17.6%), anti-HER2 directed therapy, 2 (11.8%), hormones, 7 (41.2%) and Cyclin-dependent kinase 4/6 inhibitors, 5 (29.4%). Presenting symptoms included jaw pain, infection and paraesthesia. Orthopantomogram and Computed Tomography were utilised in confirming diagnosis. The mandible was the most common site affected (52.9%).Table: 279PBaseline characteristics, risk factors and managementCharacteristicWhole cohort N=455Developed ONJ N=17Mean age (range) – yr65 (33-97)69 (49-86)Female sex454 (99.7%)17 (100%)DiagnosisEBC102 (22.4%)-MBC353 (77.6%)17 (100%)Bone modifying agentZA117 (25.7%)-Dmab334 (73.4%)16 (94.1%)Dmab -> ZA3 (0.67%)1 (5.9%)ZA -> Dmab1 (0.22%)-Risk factorsDental Intervention10 (58.8%)Hypocalcaemia3 (17.6%)Diabetes Mellitus3 (17.6%)Current Smoker1 (5.9%)ManagementConservative11 (64.7%)Additional intervention4 (23.5%)Unknown2 (11.8%)BMA discontinuedYes15 (88.2%)No2 (11.8%)Systemic treatmentContinued15(88.2%)Discontinued1 (5.9%)Switched to alternative1 (5.9%) Open table in a new tab Incidence of MRONJ is in keeping with published literature. Dental intervention during BMA treatment was our principal risk factor. High-level evidence regarding drug holidays prior to dental intervention is required.3, 4: