Effectiveness of radiation therapy on brain invasion by human papillomavirus‐related multiphenotypic sinonasal carcinoma: A case report

Human papillomavirus (HPV)‐related multiphenotypic sinonasal carcinoma (HMSC) is newly suggested and characterized by HPV‐related tumors. HMSC has a relatively good prognosis. No cases of brain invasion have been reported to date. We encountered a case of brain invasion by HMSC, in which we assessed the effectiveness of radiotherapy in comparison with biopsy and autopsy. A 69‐year‐old man was referred to a hospital three months after intracerebral hemorrhage (ICH). Contrast magnetic resonance imaging revealed a tumor in the ethmoid sinus involving the brain. We performed transnasal biopsy and intensity‐modulated radiotherapy for sinonasal and intracranial lesions. Despite radiotherapy, the patient died on day 41 after radiation. Biopsy specimens displayed mixed findings of epithelial and mesenchymal components. The tumor was immunoreactive for p16, and the RNA in situ hybridization for HPV was positive. Finally, we diagnosed the patient as having HMSC. Autopsy of the sinonasal tissue revealed a reduction in the number of tumor cells. There was a marked reduction in the number of tumor cells in the sinonasal tissue compared to that in the invaded brain tissue. The effectiveness of radiotherapy could depend on the histopathological components and location of the lesion, even in the same patient.