title: Primary osseous rhabdomyosarcoma with focal matrix formation mimicking osteosarcoma.
abstract: We present an unusual case of primary osseous pleomorphic rhabdomyosarcoma with focal matrix formation mimicking osteosarcoma. The patient was a 21-year-old man who had suffered from pain and slight enlargement of his left calf for 2 months. A plain radiograph demonstrated a large, predominantly osteolytic mass in the region of the proximal fibula with features typical of malignant primary bone tumor. On open surgical biopsy, the tumor consisted of atypical cells, some of them presenting spindle morphology. Between them, there were bands of densely hyalinized matrix with osteoid appearance, but without definite lacunae or calcifications, and an osteosarcoma was diagnosed. Consequently, the tumor was removed. The postoperative tissue presented more pleomorphic cells with some definite rhabdomyoblasts. Desmin, actin, Myf4, and MyoD1 were positive in tumor cells, and a diagnosis of rhabdomyosarcoma was eventually made. Only few cases of primary pure bone rhabdomyosarcoma have been reported. Other bone tumors with rhabdomyosarcomatous differentiation have been described: dedifferentiated chondrosarcoma, fibrosarcoma, and osteosarcoma. Our case does not meet the criteria for sclerosing rhabdomyosarcoma, as matrix formation is focal and cells are spindle-shaped and pleomorphic. However, it is a further example of a diagnostic error in connection with primary osseous tumor.
authors: Department of Oncology, Medical University of Lodz, Paderewskiego 4, 93-509, Poland.
authors: Radzislaw
authors: R
authors: Kordek
authors: Piotr
authors: P
authors: Sowa
authors: Michal
authors: M
authors: Panasiuk
authors: Marek
authors: M
authors: Kmieciak
authors: Cezary
authors: C
authors: Chudobinski
authors: Elzbieta
authors: E
authors: Pluciennik
authors: Andrzej K
authors: AK
authors: Bednarek
authors: Piotr
authors: P
authors: Potemski
authors: Dorota
authors: D
authors: Jesionek-Kupnicka
mesh_terms: D000199:Actins / Q000032:analysis; D000328:Adult; D014408:Biomarkers, Tumor / Q000032:analysis; D001859:Bone Neoplasms / Q000737:chemistry / Q000175:diagnosis* / Q000601:surgery; D003893:Desmin / Q000032:analysis; D003937:Diagnosis, Differential; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D017570:MyoD Protein / Q000032:analysis; D018008:Myogenin / Q000032:analysis; D012516:Osteosarcoma / Q000175:diagnosis*; D012208:Rhabdomyosarcoma / Q000737:chemistry / Q000175:diagnosis* / Q000601:surgery
chemical_list: D000199:Actins; D014408:Biomarkers, Tumor; D003893:Desmin; C503799:MYOG protein, human; D017570:MyoD Protein; C057363:MyoD1 myogenic differentiation protein; D018008:Myogenin