Alveolar rhabdomyosarcoma of the mandible in an adult invading the parotid gland: A rare case report

Mandibular rhabdomyosarcoma with TFCP2 rearrangement and osteogenic differentiation: a case misdiagnosed as fibrous dysplasia or low-grade central osteosarcoma

Rhabdomyosarcoma with TFCP2-related fusions (TFCP2-RMS) is a rare entity that commonly affects young adults with a predilection for skeletal involvement. We herein report a 40-year-old female patient with TFCP2-RMS who was misdiagnosed as fibrous dysplasia or low-grade central osteosarcoma of the mandible by referring institutions. Histologically, the tumor showed dominant spindle cells and focal epithelioid cells with marked immature woven bone formation. Immunophenotypically, in addition to the characteristic expression of myogenic markers, ALK, and cytokeratins, tumor cells also unusually expressed osteogenic markers, such as MDM2 and SATB2. Through fluorescence in situ hybridization, the tumor cells showed EWSR1::TFCP2 gene fusion and no MDM2 gene amplification. This is a rare case of TFCP2-RMS, which was misdiagnosed as low-grade central osteosarcoma due to its presenting immunophenotype of MDM2 and SATB2, as well as extensive osteoid matrix formation.

Metastatic Alveolar Rhabdomyosarcoma with Extensive Bone Marrow Replacement in an Older Adult

Rhabdomyosarcoma is extremely rare in adults. Metastatic rhabdomyosarcoma can resemble other malignancies, which can delay diagnosis and prompt treatment. This case illustrates an example of metastatic alveolar rhabdomyosarcoma with concurrent bone marrow infiltration. A 67-year-old woman presented with epistaxis and diffuse bone pain. She developed progressive thrombocytopenia requiring platelet transfusions. The patient was initially thought to have leukemia. She was found to have a large sinonasal mass with extensive metastatic disease and bone marrow infiltration. The patient was ultimately diagnosed with metastatic alveolar rhabdomyosarcoma. She was started on chemotherapy with vincristine, actinomycin, and cyclophosphamide. Unfortunately, she died prior to discharge home. Alveolar rhabdomyosarcoma can resemble a primary bone marrow malignancy when it infiltrates the bone marrow. Further investigation is needed to clarify its clinical behavior and expedite diagnosis and treatment.