Sclerosing pseudovascular rhabdomyosarcoma-immunohistochemical, ultrastructural, and genetic findings indicating a distinct subtype of rhabdomyosarcoma.

Sclerosing (pseudovascular) rhabdomyosarcoma in adults has been described as a rare variant of rhabdomyosarcoma characterized by extensive hyaline fibrosis and pseudovascular growth patterns. We describe another case of this rhabdomyosarcoma subtype including ultrastructural and genetic findings-the lesion presented in a 62-year-old male patient in the left lower leg. The tumor was located within the deep soft tissue with maximum diameter of 11.8 cm and skin ulceration. Ultrastructural analysis revealed irregularly distributed disorganized filaments without clear evidence of Z-bands and a richly collagenized matrix. Using comparative genomic hybridization, a sharply delineated loss of chromosomal region 10q22, loss of chromosome Y, and a gain of chromosome 18 (trisomy) were detected. Reciprocal translocations t(1;13) and t(2;13)(q35;q14) which are characteristic of alveolar rhabdomyosarcoma could be excluded. These findings, while showing a relation to other rhabdomyosarcoma subtypes, represent a relatively circumscribed genetic defect pattern in sclerosing (pseudovascular) rhabdomyosarcoma that is somewhat different from patterns described in most other rhabdomyosarcoma subtypes. Six months after tumor resection, the patient presented with metastatic disease. Further studies should concentrate on the identification of genes especially on chromosomal region 10q22 to elucidate more aspects in the pathogenesis of this rhabdomyosarcoma subtype.