Prognostic significance of Ki-67 (MIB-1) proliferation index in childhood primitive neuroectodermal tumors of the central nervous system

Background. Primitive neuroectodermal tumors (PNET) of the central nervous system, including medulloblastomas, are the most common malignant brain tum ors of childhood. Whereas some patients experience prolonged disease contro l after surgery and adjuvant therapy, others with tumors that appear com pa rable will relapse and eventually die from progressive disease. Procedure. Because proliferative activity may provide a potential correlate of biologi c aggressiveness, PNETs of 78 well-characterized patients were evaluated by Ki-67 (MIB-1) immunohistochemistry. Proliferation indicts (PI) were determ ined by counting Ki-67 (MIB-1) positive tumor cells either in the highest s taining region (hot spot PI), or in at least 15 randomly chosen fields (ran dom PI). Results. Twenty-five of 78 PNETs showed amore than twofold higher value of hot spot PI (median 9.3%; range 0.6-56'%), compared to random PI ( median 5.6%; range 0.2-41.3%). Univariate Cox regression analysis revealed that PNETs with a high hot spot PI had a significantly greater risk of prog ression and death than PNETs with a low hot spot PI (hazard ratio 1.58, P = 0.04). The hazard ratio remained significant after adjusting for M-stage i n multivariate analysis. In contrast to hot spot PI, random PI proved not t o be a significant prognostic predictor. Conclusions. Hot spot PI is a sign ificant and independent prognostic factor in PNETs. Its assessment is uncom plicated, reliable, and may supplement routine histologic examination as a means for improving the accuracy of predicting the biologic behavior of chi ldhood PNETs. Med. Pediatr. Oncol. 36:268-273, 2001. (C) 2001 Wiley-Liss. I nc.