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Abstract

Background: Soft tissue myoepitheliomas are rare and exhibit a wide spectrum of benignity and low-to high-grade malignancy with histopathological heterogeneity, including cell morphology, nuclear atypia, proliferation patterns, and background matrices, often making pathological diagnosis very challenging. Although recent molecular and genetic studies of the genetic abnormalities, particularly unique gene fusions, have determined associations with the clinicopathological features, they have not been sufficiently elucidated. Case Presentation:We present a rare case of malignant myoepithelioma that developed in the soft tissue of the groin in an elderly man, along with its macroscopic, histological, immunohistochemical and fluorescence in situ hybridization (FISH) findings. The tumor invaded the adjacent fatty tissue, but no lymph node metastasis was observed locally. Histologically, the tumor cells exhibited severe nuclear atypia, pathological nuclear mitosis, myxoid background, and rhabdoid cells. INI1/SMARCB1 nuclear loss and frequent Ki-67 and p53 positivity indicated a malignancy. Hence, we considered soft tis-Conclusion: Malignant myoepithelioma diagnosis is very challenging owing to its rarity and clinicopathological diversity. Thus, the possibility of malignant myoepithelioma should always be considered when encountering a soft tissue malignancy that is pathologically questionable, such as the present tumor, which served as a valuable and instructive case.