Unlocking the Enigma of Human Papillomavirus (HPV)-Related Multi-phenotypic Sinonasal Carcinoma: A Case With Aggressive Morphology but a Favourable Prognosis.

Human papillomavirus (HPV) is a well-known established causative agent for head and neck carcinomas, most commonly in the oropharynx. The sinonasal tract is increasingly recognised as a notable site for HPV-related carcinoma, with evidence suggesting a meaningful association with high-risk HPV. The patient is a 44-year-old female, who presented with a nasal septal growth. Initial biopsy was reported as poorly differentiated carcinoma. Subsequent excision showed malignant neoplasm with varied histomorphological patterns with areas resembling poorly differentiated carcinoma, some areas showing adenoid cystic-like features and focal pericytomatous pattern. Immunohistochemically, the neoplastic cells were diffusely positive for Pancytokeratin and p16 with a patchy expression of p63, p40, SMA, and C-KIT. The proliferation index as assessed by Ki-67 was around 35%. HPV testing by RT-PCR was positive, and the HPV-33 genotype was detected. With the given findings, a diagnosis of HPV-related multi-phenotypic sinonasal carcinoma was rendered. HPV-related multi-phenotypic sinonasal carcinoma (HMSC) shows an indolent clinical course despite an aggressive morphology. Surgery with or without radiotherapy is the recommended treatment of choice.