Primary Merkel cell carcinoma of the tongue base managed non-operatively: A case report

Merkel cell carcinoma (MCC) is a rare neuroendocrine tumour typically affecting the skin of fair-skinned or immunosuppressed, though it can affect the oral mucosa. We report the fourth documented case of MCC of the tongue in an 87-year-old male presenting with a cervical mass causing odynophagia and dysphagia. The diagnosis was confirmed through core biopsy histopathology and immunohistochemical analysis positive for CK20, synaptophysin and chromogranin. In situ hybridisation for human papillomavirus types 16 and 18 was negative, excluding HPV-driven oropharyngeal squamous cell carcinoma. Non-operative management with intensity-modulated radiotherapy and avelumab immunotherapy was commenced, inducing a complete metabolic response of the primary lesion. Thirty-three months after diagnosis, 31 months after completing initial radiotherapy, the patient is clinically well with no residual disease. Despite a dearth of documented cases, our protocol suggests that novel techniques for cutaneous MCC management with immunotherapy combined with our improved knowledge of MCC radiobiology may be successfully applied to managing locally advanced oral MCC, potentially shifting the treatment paradigm from upfront surgery toward targeted oncotherapy.