Small cell mesothelioma: A rare entity and diagnostic pitfall mimicking small cell lung carcinoma on fine‐needle aspiration

Small cell mesothelioma (SCM) is an extremely rare variant of epithelioid mesothelioma that can be mistaken for other forms of small round blue cell tumors, particularly small cell lung carcinoma (SCLC). Here, we describe a fine-needle aspiration (FNA) from a pleural lesion in a 75-year-old man with a history of known asbestos exposure. The FNA revealed cohesive clusters of uniform small round blue cells with high nuclear-to-cytoplasmic ratio, finely powdery chromatin, small inconspicuous nucleoli, and scant amount of cytoplasm. Mitoses were infrequent and nuclear molding was absent. Immunochemical profile supported a mesothelial origin, which was later confirmed by pleurectomy with a diagnosis of SCM. This report demonstrates the difficulties in cytologic evaluation of lung FNAs in differentiating SCM from SCLC or other small round blue cell tumors. As therapy differs for SCM, early recognition of the cytologic features is essential in making the correct diagnosis needed for appropriate clinical management. Diagn. Cytopathol. 2016;44:526-529. © 2016 Wiley Periodicals, Inc.