Presence of well-differentiated rhabdomyoblasts at the end of therapy for pelvic rhabdomyosarcoma: implications for the outcome.

The presence of well-differentiated rhabdomyoblasts at the end of therapy for rhabdomyosarcoma has been noted. This study was undertaken to investigate the therapeutic implications of the presence of well-differentiated rhabdomyoblasts at the end of therapy for pelvic rhabdomyosarcoma. Six patients with pelvic rhabdomyosarcoma (bladder-prostate, 4; vulvovaginal, 2) with disease diagnosed between the years 1974 and 1992 were sequentially investigated by cystoscopic or vaginoscopic examination and biopsy during and after completing therapy. All six patients received treatment according to prevailing therapeutic protocols. Biopsy material from all six patients at the end of therapy documented the presence of well-differentiated rhabdomyoblasts. Repeated biopsies demonstrated the presence of rhabdomyoblasts; however, they appeared to decrease in number with time. Mitotic activity was not observed in the biopsy materials obtained. All six patients are alive without evidence of disease from 37 to 233 months after therapy ended. The presence of well-differentiated rhabdomyoblasts at the end of therapy for pelvic rhabdomyosarcoma is a common finding. The biologic nature of these well-differentiated rhabdomyoblasts is not completely known, but they do not appear to connote the persistent presence of malignant disease and are not an indication for the continuation of therapy.