Grading of nonrhabdomyosarcoma soft tissue sarcoma in children and adolescents: a comparison of parameters used for the Fédération Nationale des Centers de Lutte Contre le Cancer and Pediatric Oncology Group Systems.

BACKGROUND

Two systems for grading soft tissue sarcoma are widely used currently: the National Cancer Institute (NCI) and the Fédération Nationale des Centers de Lutte Contre le Cancer (FNCLCC) systems. Both were developed using cohorts of predominantly adult patients. The Pediatric Oncology Group (POG) system, based on the NCI system, was adapted for grading pediatric nonrhabdomyosarcoma soft tissue sarcoma (NRSTS). The applicability and prognostic utility of the FNCLCC system in pediatric NRSTS has not been assessed or compared with the POG system.

METHODS

Tumors from 130 patients with malignant NRSTS enrolled on 3 completed multi-institutional clinical trials were assessed. Of 130 tumors, 102 (78%) were localized and 28 (22%) metastatic. Of the localized tumors, 55 of 102 (54%) were >5 cm. The estimated 5-year event-free survival (EFS) for the entire group was 47%.

RESULTS

As expected, stage and tumor sizes were predictive of EFS (P < .001). Both systems were predictive of 5-year EFS (POG, P = .0095 and FNCLCC, P = .0075). Patients whose tumors received discrepant grades (POG-G3 vs FNCLCC-G2/G1) (n = 44) had an intermediate outcome between those with concordant (G3 [n = 44] or G1/G2 [n = 42]) grades on both systems (P = .0018). By multivariate analysis, the mitotic index was predictive of EFS, using a cutoff of 10 mitotic figures per 10 high-power fields (P < .001).

CONCLUSIONS

In conclusion, both FNCLCC and POG systems provide an adequate prognostic measure of outcome for pediatric NRSTS; albeit, a sizeable subset of cases with apparently intermediate prognosis was graded differently by the 2 systems. The mitotic index appears to be a key parameter in grading pediatric NRSTS.