Mixed HPV-related Neuroendocrine Carcinoma and HPV-related Squamous Cell Carcinoma of the Base of Tongue in a Patient With Incidental Identification of Synchronous Metastatic Papillary Thyroid Carcinoma.

Background While it is not uncommon in patients with head and neck cancer to present with multiple metachronous primary neoplasms, rarely do these present as a singular mass composed of intertwined, histologically distinct malignant tumors. Sometimes referred to as collision tumors, these entities are poorly understood and only appear in a handful of case studies in the literature. Case report Here we present a 58-year-old male diagnosed with a human papillomavirus-related collision tumor consisting of oropharyngeal squamous cell carcinoma and small-cell neuroendocrine carcinoma, as well as an incidentally discovered metastatic thyroid papillary carcinoma, despite an unremarkable thyroid gland. The patient underwent transoral robotic base-of-tongue resection and partial pharyngectomy with selective neck dissection followed by chemoradiotherapy. At the 18-month follow-up the patient was doing well. His thyroid was normal and no recurrent or metastatic carcinoma was identified on the computed tomography and positron-emission tomography/computed tomography imaging findings. Conclusion To the best of our knowledge, this is the first such case in English literature. This case demonstrates the importance of tumor morphology and immunohistochemical testing in HPV-related oropharyngeal carcinomas, despite the overall good prognosis of such tumors, due to the possibility of synchronous or colliding primary neoplasms.