Fine needle aspiration biopsy diagnosis of rhabdomyosarcoma. An immunocytochemical study.

Specific antibodies against desmin, skeletal muscle actin and myosin were assessed for their usefulness in the cytodiagnosis of five rhabdomyosarcomas: one well-differentiated, two moderately differentiated and two poorly differentiated lesions. Acetone-fixed smears from fine needle aspiration biopsies and the avidin-biotinyl-peroxidase complex technique were used. All aspirates were positively immunostained with antibodies against desmin and actin. Myosin could only be detected in the moderately and well-differentiated tumors. The percentage of tumor cells positive for any of the three proteins was positively correlated with the overall degree of differentiation. However, the number of positive tumor cells decreased in the sequence desmin-actin-myosin. The results indicate the value of antibodies, especially those against skeletal muscle actin, in aiding in the cytodiagnosis of rhabdomyosarcoma, particularly with respect to its differential diagnosis from small round cell tumors in children and pleomorphic sarcomas in adults.