Remarkable Short-Term Regression of a Posterior Mediastinum Metastasis From Primary Intraosseous Carcinoma Treated With Nivolumab: A Case Report.

Primary intraosseous carcinoma (PIOC; not otherwise specified) is a rare odontogenic malignancy that is believed to arise from the odontogenic epithelium. In addition, some cases arise in odontogenic cysts or other benign precursors. There are no established treatment protocols for PIOC because of its rarity. In particular, no standard therapy has been established for patients with recurrent or metastatic PIOC. This report describes a case in which the use of nivolumab showed a marked treatment response in metastatic PIOC. The patient was a 71-year-old man with PIOC. The patient underwent segmental mandibulectomy with modified radical neck dissection after neoadjuvant chemotherapy, including 2 cycles of paclitaxel, cetuximab, and carboplatin and 1 cycle of docetaxel, cisplatin, and 5-fluorouracil. The lesion rapidly enlarged during neoadjuvant chemotherapy, and surgical specimens showed no histologic therapeutic effects of chemotherapy. Three months after the surgery, contrast-enhanced computed tomograms showed posterior mediastinal lymph node metastasis. Treatment with nivolumab was initiated, and notable clinical improvement was noted after 2 cycles. Although it was a short-term treatment, remarkable effects were observed and no adverse events were noted during and after nivolumab treatment. Nivolumab could be an attractive treatment option for metastatic PIOC that is resistant to traditional chemotherapy and target therapy, including cetuximab. Further investigation of this treatment is warranted.