Evolving significance of prognostic markers associated with new treatment strategies in neuroblastoma

Abstract

The striking differences in the natural history of clinical subgroups of neuroblastoma (NB), and the evolving therapeutic approaches for each, makes it imperative for prognostic markers to be reevaluated within individual clinical categories. At least one third of NB cases present without distant metastasis and cytotoxic therapy does not alter the natural history. We carried out a retrospective analysis of archived tumor samples. Fifty-seven of these patients had local-regional (LR) NB and were managed conservatively, initially treated with surgery alone. Among the biologic and clinical features analyzed including age, stage, histology, ploidy, MYCN, and 1p36, 1p22, 11q, 14q, 9p and 19q loss of heterozygosity (LOH) in multivariate analysis, diploidy was one of the most significant factors associated with progression-free survival and stage 4 progression. Clonal ploidy heterogeneity was common in LR NB. A predominant near-triploid clonal population was found in most cases of non-progressing LR NB tumors whereas progressing LR NB cases had a predominant diploid clone. We also reviewed the prognostic factors among 84 stage 4 NB cases treated with the N5, N6 or N7 protocols at MSKCC from 1987 to 1999. Traditional markers such as lactate dehydrogenase (LDH), ferritin, age and MYCN status were not prognostic in the univariate analysis. 11q23 and 1p22 LOH were correlated with better survival. These results highlight the evolving significance of prognostic analysis in homogeneous clinical groups undergoing similar treatments. To further characterize the gene expression profile between local-regional and metastatic NB, we carried out Microarray analysis of 41 NB tumors and 12 NB cell lines, using the Affymetrix Genechip Human Genome U95 Set^™. Distinct gene expression patterns between metastatic and non-metastatic NB tumors have been identified. Validation of these results and further mechanistic studies may shed new light on the biology of metastasis in human NB.

Introduction

Clinical observations throughout the last 15 years at MSKCC and world-wide support the separation of neuroblatoma (NB) into at least three distinct biologic groups, i.e. metastatic stage 4 in >1 year of age, infant stage 4, and non-stage 4 (International Neuroblastoma Staging System (INSS) stages 1, 2, 3 and 4s). Because of the striking differences in the natural history of these clinical subgroups of NB, and the radically different approaches for each, prognostic markers are most meaningful when analyzed within individual clinical categories. Furthermore, when challenged by improving outcome, the clinical utility of individual clinical and genetic features deserves constant reevaluation.

It is generally believed that the diverse clinical behaviors of NB result from the capacity of these tumors to exploit their genetic malleability to evolve and adapt. NB is a genetically heterogeneous neoplasia and intratumoral heterogeneity and clonal evolution have been shown to be a frequent occurrence [1]. Study of the molecular genetics of NB has elucidated several non-random genetic events associated with the disease: allelic losses on chromosomes 1p, 11q, 14q, 9p, 9q, 2q, 3p, 4p and 18q implicating putative tumor suppressor genes; allelic gains on chromosomes 17q, 18q, 1q, 7 and 5q, some related to growth control genes; amplification of the oncogene MYCN; and changes in the normal diploid chromosomal content [2]. The clinical importance of each of these genetic events and their evolution during tumor progression are, however, largely unknown. Except for MYCN status, the relationship of each of these individual genetic events to the clinical course of NB has not been firmly established. Furthermore, although some are strongly associated with survival or progression-free survival for NB as a whole, their significance for individual categories of NB as described above remains unclear. Thus, their utility remains uncertain in the management of individual patients.

We carried out a retrospective analysis of archived tumor specimens from patients with neuroblastoma treated at MSKCC. We studied the prognostic importance of biologic markers within each clinical group and attempted to define the genetic-molecular profile of metastatic versus local-regional NB.