Proliferation index revisited in neuroblastic tumors

Neuroblastic tumors (NB) are the most common extracranial pediatric neural crest-derived tumors, with a dismal outcome in a substantial group of patients. The study objective was to evaluate the patho-clinical correlations and prognostic impact of the proliferation index (PI) measured with two markers, Ki67 and topoisomerase II alpha (Topo2A), in a NB series. A retrospective analysis of 118 NB from 103 consecutive patients was performed. Analyzed data included tumor stage, histology, mitosis/karyorrhexis index (MKI), MYCN status, and overall survival. Patients' median follow-up period was 50 months. Ki67 and Topo2A PI were assessed immunohistochemically on representative tissue slides in hot spots. PI for Ki67 was in the range 0-72% (median 18%) and for Topo2A was in the range 0-58% (median 20%), being strongly interrelated (r = 0.83). Median PIs with both markers were lower in children older than 18 months (> 18 m) than in the younger patients, with p = 0.0002 and p = 0.005 respectively. Higher Ki67 and Topo2A correlated with metastatic stage, higher MKI, and inversely with increasing tumor differentiation. The cut-off values of PI Ki67 > 30% and Topo2A > 20% were associated with fatal outcome of the disease. In the subgroup of patients > 18 m already at cut-offs Ki67 > 10% and Topo2A > 15% a fatal outcome was predicted by Kaplan-Meyer analysis. Cox regression analysis identified cumulative PI (joint Ki67 and Topo2A index) as an independent prognostic factor. The conclusion is that the proliferation index measured with the examined markers provides substantial prognostic information in NB, especially in infants. PI assessment should become an element of the standard pathological checkup list of NB tumors.