Fine-needle aspiration cytology of retroperitoneal myoepithelial carcinoma: A rare encounter with diagnostic dilemmas.

Myoepithelial carcinoma (MC) arises from the myoepithelial cells. It is a rare tumor with a predilection for salivary glands. MC in soft tissue is uncommon. Soft tissue MC exhibits dual epithelial and smooth muscle phenotype. The extremities and limb girdles are commonly affected. We present cytological findings of retroperitoneal MC with an accurate diagnosis being rendered with the aid of immunocytochemistry on the cell block and demonstration of EWSR1 rearrangements by fluorescence in situ hybridization on cytology smear. The smears were cellular, showing loose clusters and sheets of tumor cells embedded in dense eosinophilic to myxoid matrix material. The cells were oval to polygonal, with focal areas showing moderate nuclear pleomorphism, vesicular to coarse chromatin, and vacuolated cytoplasm with clearing. On immunocytochemistry, tumor cells were positive for epithelial membrane antigen, pan-cytokeratin, calponin, smooth muscle actin, and S-100. A literature review shows only a handful of cases of soft tissue MC. The current report emphasizes the need for cytomorphological awareness with the employment of ancillary testing for accurately diagnosing this rare tumor at an uncommon location. We also discuss the diagnostic challenges and troubleshooting.