Mandibular bone regeneration after marginal mandibulectomy for advanced MRONJ following denosumab discontinuation: a case report.

Background: Medication-related osteonecrosis of the jaw (MRONJ) is a serious complication associated with bone-modifying agents, including denosumab. The clinical course after denosumab discontinuation remains insufficiently understood, and optimal surgical strategies for advanced cases are still under debate. Case presentation: We report a 71-year-old man with castration-resistant prostate cancer and multiple bone metastases who developed MRONJ during denosumab therapy for more than 3 years. After diagnosis at our institution, denosumab was discontinued based on the decision of the treating oncologist. Rapid progression of bone resorption was observed within several months, in which discontinuation of denosumab may have been a contributing factor. Although segmental mandibulectomy was considered, the patient declined radical surgery. Marginal mandibulectomy was therefore performed via an intraoral approach, with preservation of the lingual bone plate and periosteum. During long-term follow-up, marked bone regeneration became evident by 2 years postoperatively and was sustained at 6 years, with restoration of mandibular continuity. No recurrence of MRONJ or new skeletal-related events was observed during ongoing oncological follow-up. Conclusion: Discontinuation of denosumab may have contributed to rapid osteolytic progression in MRONJ. Preservation of biological structures during marginal mandibulectomy, as part of multidisciplinary management, may be associated with favorable bone regeneration. These findings highlight the complexity of MRONJ management and the importance of individualized, multidisciplinary approaches.