Merkel cell tumor-like neuroendocrine carcinoma associated with the submandibular gland. Report of a case with cytologic, immunohistochemical, electron microscopic and flow cytometric studies.

We report a rare case of primary Merkel cell tumor (MCT)-like neuroendocrine carcinoma (i.e., small cell carcinoma) associated with the submandibular gland in a 73-year-old man. Despite the lack of a known skin primary, the tumor exhibited cytomorphologic (predominant single cells with "intermediate filament buttons" in the background), ultrastructural (dense core granules and a globular aggregate of intermediate filaments) and immunohistochemical (paranuclear globular coexpression of cytokeratin and neurofilaments) features identical to that of MCT. The tumor contained an aneuploid peak with DNA index of 1.1 and an S phase of 20.5%. The tumor measured 5.8 cm and was situated between the skin and submandibular gland, with which it was closely associated but separated by connective tissue. The literature on MCT without a known skin primary is reviewed, and the cytomorphologic features that allow the distinction between MCT, lymphoma and oat cell carcinoma are discussed.