Primary Merkel Cell Carcinoma of the Submandibular Gland: When CK20 Status Complicates the Diagnosis

Abstract

Merkel cell carcinoma is a neuroendocrine tumor that occurs predominantly on the sun-exposed skin, with rare cases in the extracutaneous sites. It represents one of the extremely rare malignant neuroendocrine tumors of the salivary glands. We report a case of primary Merkel cell carcinoma of the right submandibular gland. The preoperative diagnosis was doubtful and the definitive histological diagnosis proved to be very difficult considering the extreme rarity of this tumor. The intraoperative evaluation of the macroscopic characteristics of the lesion led to an elective lymph node dissection. The extreme aggressiveness of the disease has resulted in the necessity of a new post-operative staging and in a multimodal treatment. This is the first primary submandibular gland Merkel cell carcinoma described in the literature. Differential diagnosis may be challenging and proper hematoxylin-eosin staining and immunohistochemical studies are mandatory.

Fig. 1

Preoperative contrast-enhanced MR (VIBE sequence) on coronal (a) and axial plane (b) showing a 22-mm nodule (asterisk) with sharp margins and non-homogeneous enhancement within the right submandibular gland

Fig. 2

Histologic features of the tumor (hematoxylin-eosin): epithelioid cells organized in nests with fibrous strands interposed, showing round ovular nuclei with finely scattered chromatin and scarce cytoplasm (a). Perineural spread: tumor cells invading the perineurium (b). Intravascular growth: clot of neoplastic cells inside the lumen of a small vessel (c). Nodal metastasis with extranodal extension: residual lymphoid parenchyma invaded by malignant cells; infiltrated fat tissue is also visible (d)

Fig. 3

Tumor cells show strong and diffuse positivity for CK14 staining (4x) (a) and cytoplasmic and peri-nuclear positivity for Chromogranin A staining (10x) (b). MCPyV staining (10x): granular nuclear positivity for specific Merkel Cell polyomavirus large T antigen (c). CK20 staining (10x): tumor cells are completely negative (d)