Immature teratomas in children: pathologic considerations: a report from the combined Pediatric Oncology Group/Children's Cancer Group.

Pediatric germ cell tumors (n = 135) with a major component of immature teratoma (IT) registered on Pediatric Oncology Group/Children's Cancer Group treatment protocols from 1990 to 1995 were reviewed. Sixty cases were pure IT with no malignant component and 75 were mixed tumors with a major component of IT. Foci of yolk sac tumor (YST) were present in all 75 mixed tumors; additional malignant components were present in 15. The IT component was as follows: 47% grade 3, 29% grade 2, 24% grade 1. There were no significant correlations between tumor grade and patient age by specific subsets or overall (all p > 0.10). Significant correlations were detected between stage and the presence of foci of YST (p = 0.0145) and grade and the presence of foci of YST (p < 0.001). Serum alpha-fetoprotein concentrations were elevated at diagnosis in 96% of ovarian tumors with foci of YST and were mildly elevated (< 60 ng/dL) in only 16% of tumors without YST. Overall 2- to 6-year survival rate was 96% and was related to the presence of YST. Central pathologic review revealed aspects of morphologic diagnosis that were most frequently misinterpreted by contributing pathologists. These included the classification of differentiating tissues as immature and the failure to recognize two well-differentiated patterns of YST (the hepatoid pattern resembling fetal liver and the well-differentiated glandular pattern resembling fetal lung or intestine). Such foci were often overlooked. The authors conclude that the presence of microscopic foci of YST, rather than the grade of IT, per se, is the only valid predictor of recurrence in pediatric IT at any site.