Tumor-cell DNA content predicts outcome in children and adolescents with clinical group III embryonal rhabdomyosarcoma. The Intergroup Rhabdomyosarcoma Study Committee of the Children's Cancer Group and the Pediatric Oncology Group

PURPOSE The prognostic value of tumor-cell DNA content (ploidy) was evaluated in children with unresectable, nonmetastic rhabdomyosarcoma of embryonal histology. PATIENTS AND METHODS Flow-cytometric techniques were used to estimate the ploidy of tumor specimens from 34 patients with embryonal rhabdomyosarcoma who were enrolled in the intergroup rhabdomyosarcoma study III (IRS III) from 1985 to 1991. Tumors were classified as diploid or hyperdiploid (DNA content, 1.1 to 1.8 times that of normal diploid cells). The influence of ploidy on clinical outcome was assessed by the Kaplan-Meier technique and Cox regression analysis with stepwise selection. RESULTS Twelve of the tumor specimens were diploid and 22 were hyperdiploid. The patient groups defined by diploid or hyperdiploid tumors had similar presenting characteristics (eg, age, tumor size, and anatomic site). Significantly more children with hyperdiploid tumors achieved a complete response than did children with diploid tumors (85% v 42%; P = .01). The probability of progression-free survival at 5 years (+/- SE) was 91% +/- 6% for the hyperdiploid group, compared with 17% +/- 11% for the diploid group (P < .001). Hyperdiploidy was also associated with a significantly higher overall survival rate at 5 years: 96% +/- 4% versus 50% +/- 14% (P = .004). Ploidy retained its prognostic significance after adjustment for tumor site in the Cox regression model. CONCLUSION Tumor-cell ploidy strongly correlates with outcome in children with nonmetastic, unresectable embryonal rhabdomyosarcoma. The two biologically distinct groups identified by this measure would benefit from further refinements in risk-directed therapy.