Abstract

Clear cell mesenchymal neoplasm (CCMN), also referred to as distinctive dermal clear cell mesenchymal neoplasm, is a very rare intradermal tumor of uncertain cell lineage. It is a diagnosis of exclusion and it is morphologically similar to lesions such as metastatic clear cell renal cell carcinoma. To our knowledge, only 6 cases, in adults aged 38-71 years, have been described previously in the literature. This tumour has never been reported in the pediatric population. We report a case of CCMN in a 15-year-old female who presented with a 1.2 cm raised lesion on the posterior knee. Histological sections show an intradermal tumor composed of nested epithelioid cells with abundant clear cytoplasm, prominent nucleoli, and a network of thin-walled blood vessels. There is absence of necrosis and nuclear pleomorphism and no mitotic figures are identified. PAS and PAS-D stains show intracytoplasmic glycogen. By immunohistochemistry tumor cells show positive membranous and occasional cytoplasmic staining for NK1/C3 (CD63) in addition to strong and diffuse membranous staining for CD10. Negative immunostains include, S100, SOX10, Melan-A, HMB-45, pancytokeratin (CK 8/18 + AE1/AE3), synaptophysin, chromogranin, CD56, ERG, CD163, EMA and GFAP. These findings are consistent with the reported features of CCMN, as originally described in 2004 by Lazar et al..

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