New definitions of focal and diffuse anaplasia in Wilms tumor: The International Society of Paediatric Oncology (SIOP) experience

Background, Unlike the original definitions of focal (FA) and diffuse anapl asia (DA) in Wilms tumor (WT), recently redefined FA and DA proved to be of prognostic significance. The aim of the study was to analyze WT from the S IOP file, the majority of which were treated with preoperative chemotherapy , in order to investigate whether chemotherapy influenced the presence of a naplasia, whether the new definitions were applicable to these tumors, and whether they were of prognostic significance. Procedure. The unilateral ana plastic WT of children up to 16 years of age from the SIOP 6 and 9 nephrobl astoma trials and studies were first classified according to the original d efinitions and analyzed. Then they were reclassified and analyzed according to the new definitions. Results. Anaplasia was diagnosed in 86 (5.5%) of 1 ,554 unilateral WT. The age at diagnosis ranged from 9 to 175 months (media n, 63) and more than half of children were over 5 years of age. From 15% to 85% of the tumor mass showed chemotherapy-induced changes. Blastemal anapl asia was seen in 74, stromal in 23, and epithelial in 22 cases. According, to the original definitions, FA was diagnosed in 55 (64%) and DA in 31 (36% ) cases. In total, 48% children were alive and well, including 53% with FA and 39% with DA (P = 0.23). When reclassified, 39 old FA cases were moved t o the new DA group, resulting in 70 (81%) DA and 16 (19%) FA cases. The fem ale-to-male ratio for FA changed from 1.9:1 to 1:1 while remained unchanged for DA. The percentage of FA stage I cases increased from 31% to 44%, whil e it decreased from 25% to 6% for stage III. For other stages it remained v irtually unchanged. The overall 4-year actual survival was 75% for FA and 4 1% for DA (P = 0.03). Conclusions, Preoperative chemotherapy did not oblite rate or produce anaplasia. The new definitions were applicable to pretreate d cases and they were of prognostic significance. Med. Pediatr. Oncol. 32:3 17-323, 1999. (C) 1999 Wiley-Liss, Inc.