Prevalence and clinical impact of anaplasia in childhood rhabdomyosarcoma : a report from the Soft Tissue Sarcoma Committee of the Children's Oncology Group.

BACKGROUND: Anapalsia is rare in childhood rhabdomyosarcoma and has not been included in the International Classification of Rhabdomyosarcoma (ICR). A recent review of cases from the Soft Tissue Sarcoma Committee of the Children's Oncology Group (COG) suggests that anaplasia might be more common than previously reported and may impact clinical outcome.

METHODS: The prevalence of anaplasia (focal or diffuse) was prospectively assessed in 546 eligible cases who were registered in an Intergroup Rhabdomyosarcoma Study Group (IRSG) or COG therapeutic trial from 1995 through 1998. The incidence of anaplasia in tumor samples and its impact in predicting clinical outcome was assessed.

RESULTS: Overall, 71 (13%) of all samples analyzed had anaplasia. Anaplasia was more common in patients with tumors in favorable sites and was less commonly observed in younger patients and in those with stage II, III, or clinical group III disease. Regardless of its distribution (focal or diffuse), on univariate analysis the presence of anaplasia negatively influenced the failure-free survival rate (63% vs 77% at 5 years) and overall survival (68% vs 82% at 5 years) rates in patients with embryonal rhabdomyosarcoma. This effect was most pronounced in children with intermediate-risk tumors. Anaplasia did not affect outcome in patients with alveolar tumors.

CONCLUSIONS: The incidence of anaplasia in patients with rhabdomyosarcoma is higher than previously described and may be of prognostic significance in children with intermediate-risk embryonal rhabdomyosarcoma.