39. HPV-related multiphenotypic sinonasal carcinoma, an emerging entity in an unusual location: A case report

Abstract

Background: Human papillomavirus (HPV)–related multiphenotypic sinonasal carcinoma (HMSC), originally known as HPV-related carcinoma with adenoid cystic carcinoma-like features, is a distinct tumour recently described in the sinonasal tract. This peculiar tumour exhibits morphologic features of a salivary gland tumour including admixed ductal and myoepithelial elements, as well as displays an unusual pattern of surface involvement with atypical squamous cells. It is associated with high-risk HPV. Most cases usually present as a large and destructive sinonasal mass with high-grade histologic features. Aim: We present a case report of HMSC arising in the floor of mouth of a 57-year-old Chinese man. Methods (clinical history): The patient was an ex-smoker who presented with a floor of mouth ulcer. The lesion was biopsy and was called a submucosal adenoid cystic carcinoma. Subsequently, the patient underwent wide resection of floor of mouth tumour, marginal mandibulectomy and neck dissection. Results (pathological findings): Macroscopic examination revealed an ulcerative tumour measuring 2.5 cm, extending to the margins. Microscopically, the tumour was composed of basaloid cells showing variable growth patterns including a cribriforming pattern that closely resembles adenoid cystic carcinoma. It was continuous with the mucosa that showed dysplastic squamous epithelium. On immunohistochemistry, the myoepithelial cells were positive for the myoepithelial markers. p16 was positive in both squamous and epithelial components. Metastatic carcinoma was present in two of the harvested lymph nodes. The patient developed pulmonary and liver metastases after two years of follow-up, which were confirmed histologically. Conclusions: This is the first case of HMSC reported in the floor of mouth, which behaves more aggressively as opposed to those arise from the sinonasal tract. It is important to recognise HMSC as they have a different clinical behaviour. The clue to the diagnosis is recognising the atypical squamous cells on the surface, corroborated by p16 positivity in tumour cells.