Merkel cell carcinoma is the cutaneous counterpart of small cell carcinoma, and the most important differential diagnosis is cutaneous metastasis of small cell carcinoma of the lung. There have been a handful of studies reporting on the utility of a variety of immunohistochemical markers that distinguish between the two entities. Achaete-scute complex-like 1 (MASH1, ASCL1) is important in the development of the brain and the diffuse neuroendocrine system including pulmonary neuroendocrine cells. A recent study, using a cDNA array, identified Mash1 as one of the best classifier genes to differentiate pulmonary small cell carcinoma from Merkel cell carcinoma. We immunohistochemically applied this finding to the diagnostic setting. A total of 30 cases of Merkel cell carcinoma and 59 cases of small cell carcinoma of the lung were immunostained with anti-MASH1 and TTF-1 antibodies. Of 59 small cell carcinomas, 49 (83%) expressed MASH1 in nuclear staining whereas out of 59 small cell carcinomas, 43 (73%) expressed TTF-1 in nuclear staining. MASH1 was completely negative in all 30 Merkel cell carcinomas whereas TTF-1 expression was seen in 1 of the 30 Merkel cell carcinomas (3%). MASH1 is a useful adjunct marker for differentiating small cell carcinoma of the lung from Merkel cell carcinoma.
Abstract:Spindle cell and pleomorphic lipoma constitute a spectrum of lipomatous lesions with characteristic clinical, morphologic, immunohistochemical, and molecular features. Multiple variants have been previously described including vascular, fibrous, plexiform, and those with significantly less fat termed “low-fat” and “fat-free” by Folpe. Cytogenetically, spindle cell lipomas frequently display monoallelic loss of 13q14 region, an abnormality also found in cellular angiofibroma and mammary-type myofibroblastoma. Pseudoangiomatous spindle cell lipoma, originally described by Fletcher et al in 1994, is a rare variant within the spindle cell/pleomorphic lipoma spectrum, with less than 20 published cases. It consists of an admixture of spindle cells, “ropey” collagen, variable amounts of mature fat, and irregular, branching slit-like vascular spaces. The authors present a case of a 1-cm subcutaneous lesion excised from the neck of a 70-year-old man with classic histologic and immunohistochemical features of “low-fat” pseudoangiomatous spindle cell lipoma. Fluorescence in situ hybridization demonstrated a loss of 13q14 region, a characteristic presumed cytogenetic finding of spindle cell lipoma, which has been previously unconfirmed in this variant.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.