Primary Merkel cell carcinoma of the parotid gland: a rare clinical entity
CR24
Sangeetha Yogarajah
Sangeetha Yogarajah (1), Ann Sandison (2), Aleix Rovira (3), Barbara Carey (3)
Merkel cell carcinoma (MCC) is a rare neuroendocrine tumour typically arising in skin. Almost 50% of cutaneous tumours arise in head and neck, usually in the elderly. MCC is biologically aggressive, with frequent local recurrence, regional lymph node and distant metastasis. De novo MCC at non-cutaneous sites is rare. We report a case of primary MCC of the parotid gland.
A 42-year-old male presented to the Head and Neck department with a 2-month history of a painless mass involving the left parotid. The mass was stable in size with no numbness, paraesthesia or facial palsy described and no relevant background medical history. He was a non-smoker and did not consume alcohol. On examination, a firm non-tender fixed 3cm mass was noted over the left parotid. Cutaneous examination was normal.
Ultrasound revealed a 29 x 15 x 20mm well-defined hypoechoic lesion in left parotid gland with internal vascularity. FNA was in keeping with a small cell carcinoma but immunostaining for CD45, chromogranin and TTF1 did not support a primary or metastasis from lung. Core biopsy demonstrated high-grade carcinoma, strongly positive for cytokeratins CK5/6 and CK7 and CK20 with characteristic nuclear dot positivity. CD56 was positive and proliferation index with MIB1 immunostain estimated 80%. Polyoma virus immunostain was positive. MRI and PET-CT showed no distant metastases or separate primary metabolically active tumour. The patient underwent left conservative parotidectomy, neck dissection with adjuvant radiotherapy.
In conclusion, primary MCC of the parotid gland is extremely rare. Only 4.5% of MCCs arise at non-cutaneous sites. There is considerable diagnostic confusion between primary and metastatic parotid gland MCC since morphology and immunohistochemical profile is essentially the same. Specialist histopathological assessment and exclusion of primary lesions through a thorough clinical history and cutaneous exam are essential. Multimodal treatment is recommended.
