SAT-734 Unmasking a Rare Risk: Osteonecrosis of the Jaw Following Pembrolizumab Therap

Abstract Disclosure: T. John: None. G. Patel: None. P. Lekprasert: None. K.K. Win: None. Introduction: The use of pembrolizumab, a programmed death receptor-1 (PD-1) inhibitor, has significantly expanded in recent years, making it the most commonly used oncology drug for solid tumors. Recent case reports have highlighted osteonecrosis as an emerging but notable complication associated with pembrolizumab use; however, it is essential to note that such cases are rare, underscoring the need for vigilance. The mechanism behind this process is complex and multifactorial. It is suspected to be due to immune modulation, suppression of osteoclast formation, and the uncoupling of osteoclast and osteoblast activity. We herein report a case of pembrolizumab-related osteonecrosis of the jaw in a patient who received immunotherapy for breast cancer treatment. CASE PRESENTATION: The patient is a 49-year-old female with a medical history of hypertension, hyperlipidemia, hypothyroidism, heart failure with preserved ejection fraction, neurofibromatosis type 1, and left-sided breast cancer. She had undergone neoadjuvant chemotherapy and immunotherapy, receiving eight cycles of pembrolizumab, followed by lumpectomy, adjuvant radiation, and nine additional cycles of pembrolizumab. Four months after completing immunotherapy, she presented with complaints of spontaneous loss of four upper molar teeth, accompanied by a prolonged dull ache in the surrounding area. The patient denied alcohol or tobacco use and had no other risk factors for osteonecrosis. Additionally, she had no history of prolonged or high-dose systemic steroid use, nor had she been treated with denosumab or bisphosphonates. On intraoral examination, there was moderate recession of multiple teeth and an area of exposed bone, findings highly suggestive of osteonecrosis. Several carious teeth and a fractured tooth, which required extraction, were also noted. A panoramic dental x-ray revealed generalized bone loss. Given the temporal relationship between her symptoms and recent immunotherapy, she was diagnosed with suspected medication-related osteonecrosis of the jaw (MRONJ) secondary to pembrolizumab use. The patient was educated on proper dental hygiene practices, and follow-up appointments over the next year showed a complete resolution of her symptoms. Conclusion: This rare case highlights a serious potential complication of pembrolizumab. An increased awareness and multi-disciplinary approach is essential for early detection and effective management. Presentation: Saturday, July 12, 2025