LAUSR

OBJECTIVE The aim of this study was to prospectively determine the incidence of medication-related osteonecrosis of the jaw (MRONJ) and define risk factors in patients with metastatic breast cancer treated with zoledronic acid and/or denosumab. STUDY DESIGN In a prospective cohort study performed in Region Skåne, Sweden, from January 1, 2012, until December 31, 2015, all patients with breast cancer who had radiographic evidence of bone metastases and were treated with zoledronic acid or denosumab were included and followed up until May 31, 2018. RESULTS Of the 242 patients, MRONJ developed in 16 (6.6%) during the 77 months of study. The incidence of MRONJ in patients treated with zoledronic acid was 4.1%, and in patients treated with denosumab, it was 13.6%. The risk of MRONJ was higher in patients on denosumab than in those treated with zoledronic acid (P = .011). Corticosteroid use was associated with a decreased risk of MRONJ (P = .008), and diabetes was associated with an increased risk of MRONJ (P = .02). CONCLUSIONS The incidence of MRONJ is 6.6% (>3 times higher) in denosumab-treated patients with breast cancer compared with that in patients treated with zoledronic acid. Corticosteroid use decreased the risk of MRONJ.