Spindle cell rhabdomyosarcoma in adults: clinicopathological and immunohistochemical analysis of seven new cases.

Rhabdomyosarcoma (RMS) is currently classified into embryonal RMS, including its botryoid and spindle cell variants, alveolar RMS, including a solid variant, and pleomorphic RMS. In children and adolescents embryonal RMS occurs in a younger age group than alveolar RMS, and pleomorphic RMS is almost always seen in older adults. Most recently rare spindle cell and sclerosing, pseudovascular RMS have been reported in adults as well. We analysed the clinicopathological and immunohistochemical features of seven new cases of spindle cell RMS arising in adult patients. Five patients were male and two were female and the age of the patients ranged from 38 to 76 years. Four neoplasms arose on the lower extremities and one case each on the forearm, the lateral aspect of the neck and the penis. Five neoplasms were completely excised, in one incompletely excised neoplasm additional chemotherapy was given, and in one patient a biopsy was done only so far. All neoplasms arose in subcutaneous and deep soft tissues with dermal involvement in one case, and the size of the neoplasms ranged from 4 to 19 cm in largest diameter. Histologically, a plump or diffuse infiltration was seen, and all neoplasms were mainly composed of cellular bands and fascicles of atypical spindle-shaped tumour cells containing enlarged and atypical nuclei associated with a variable number of rhabdomyoblasts. In addition, focal areas reminiscent of sclerosing, pseudovascular RMS were noted in three cases, and in two cases each small solid areas with pleomorphic tumour cells as well as scattered round tumour cells were present. Proliferative activity ranged from 1 to 60 mitoses in 10 high-power fields and tumour necrosis was evident in four cases. Immunohistochemically, all neoplasms tested stained variably positive for desmin, myf-4, WT1 and CD 99, whereas fast myosin was positive in only two out of seven cases. In addition, five out of seven cases tested stained focally positive for alpha-smooth muscle actin. The remaining antibodies (h-caldesmon, S-100 protein, CD 34, pancytokeratin and epithelial membrane antigen) were all negative. Follow-up information was available in five patients (range from 10 to 48 months) and revealed lung metastases in two patients who died of disease within a short period. In summary, spindle cell rhabdomyosarcoma represents a rare neoplasm in adulthood characterized clinically by a rather poor prognosis, and shows a broad morphological spectrum including most likely the sclerosing, pseudovascular variant. Immunohistochemically, tumour cells in RMS stain positively for CD 99 and WT1 as well, which is of importance in the differential diagnosis to other mesenchymal neoplasms, whereas fast myosin does not represent a reliable marker for RMS in adults.