[Myxoinflammatory fibroblastic sarcoma of the lower limb]

Myxoinflammatory fibroblastic sarcoma (MIFS) is a rare, low-grade, painless tumor of mesenchymal origin. In the current, 5th edition of the World Health Organisation (WHO) 'Classification of tumors: Soft tissue and bone tumors', there is no exact diagnostic genetic alteration defined in MIFS. Hereby we present the case of a 71-year-old female patient, with a medical history of benign essential hypertension, who visited the hospital because of a lesion above her right shin. She perceived the lesion 1.5 years prior to the medical attendance, and she only attended the medical facility because of the development of pain, erosion and papule formation on the skin surface. Microscopically, the lesion had cellular and pleomorphic appearance with nodular structure, and showed honeycomb-like infiltration of the subcutaneous fat tissue. Tumor cell infiltration was visible among the collagen fibers of the dermis. Tumor cells frequently displayed multinuclear morphology with prominent, viral inclusion-like nucleoli and exuberant fibrillary, often vacuolated and ground-glass cytoplasm. With immunohistochemical examination, tumor cells showed multifocal positivity with CD34, CD31, podoplanin (D2-40), cyclin D1, and epithelial membrane antigen (EMA). Furthermore, the tumor cells proved to be diffusely positive with smooth muscle actin (SMA). After meeting all the essential criteria of the current WHO classification, the case was concluded as MIFS, showing high-grade features. According to our experience, an immunohistochemistry panel of podoplanin, ciklin-D1, CD10, EMA, CD34, and CD31 can facilitate the correct conclusion. Our case of MIFS highlights the unusual, focally high-grade features of this complicated, challenging disease. Diffuse SMA positivity is a known, but uncommon feature of these tumors. Orv Hetil. 2023; 164(41): 1637-1641.