Epithelioid and spindle cell rhabdomyosarcoma with EWSR1::TFCP2 fusion mimicking metastatic lung cancer: A case report and literature review

Rhabdomyosarcoma (RMS) with EWSR1/FUS::TFCP2 fusion is an emerging, molecularly defined, rare subtype of RMS. It can affect patients in a wide age range and follows an aggressive clinical course according to the reported cases. Due to its unusual clinical and pathohistological features, with a typical intraosseous presentation and common cytokeratin expression, the diagnosis is challenging, and metastatic undifferentiated/sarcomatoid carcinoma can be an important differential diagnosis. We report here a case of a 55-year-old woman with an RMS with EWSR1::TFCP2 fusion mimicking metastatic lung cancer in view of the clinical and microscopic presentation. However, further molecular workup, including RNA sequencing, led to the proper diagnosis. Although these tumors are rare, knowledge of their unique features is essential for correct diagnosis as a basis for clinical management and optimization of therapeutic approaches.

Intraosseous rhabdomyosarcoma of the maxilla with TFCP2 fusion: A rare aggressive subtype with predilection for the gnathic bones

Rhabdomyosarcomas (RMS) are malignant tumors with skeletal muscle differentiation extremely rare in intraosseous sites. We reported a rare case of an aggressive intraosseous RMS found in the maxilla of a 17-year-old female patient with five months of evolution. Computed tomography revealed a large osteolytic lesion extending from tooth 21 to 27, causing buccal and lingual cortical plate perforation. Microscopically, the lesion showed a proliferation of spindle-shaped cells with elongated nuclei and eosinophilic cytoplasm, arranged in an interlaced fascicle pattern. The nuclei ranged from vesicular with distinct nucleoli to hyperchromatic. A focal component of plump to epithelioid cells with a moderate amount of eosinophilic cytoplasm was seen at the periphery of the tumor. The immunohistochemical analysis revealed positivity for desmin, MyoD1, and myogenin (scattered cells). S-100, SOX10, HMB45, β-catenin, and CD34 were negative. Ki-67 was positive in 30% of tumor cells. Fluorescence in situ hybridization (FISH) analysis showed the presence of a FUS-TFCP2 fusion. The diagnosis was intraosseous RMS with TFCP2 fusion. Surgical excision followed by chemo- and radiotherapy was carried out; however, the patient died of disease nine months after the treatment. Because of the rarity and non-specific signs and symptoms, the clinical diagnosis of intraosseous RMS is difficult and often overlooked. Therefore, careful histopathological evaluation, supported by immunohistochemical and molecular analysis, is essential to correct diagnosis. Early surgical excision with tumor-free margins and prolonged follow-up are strongly recommended.