Molecular analysis of the 9p21 locus and p53 genes in Ewing family tumors

The EWS-ETS rearrangements, and their respective fusion gene products, are specifically associated with histopathologically Ewing family tumors (EFT). These translocations are implicated in generating malignant transformation of EFT, but the presence of additional genetic alterations must be conside red in the pathogenesis of such tumors. We analyzed 26 samples (biopsies an d/or nude mice xenotransplants) collected from 19 patients with an EFT to d etermine whether molecular and cytogenetic alterations of the G(1)/S checkp oint genes are implicated in the pathogenesis of EFT. We found inactivating p53 mutations in three (16%) cases, which correlated with a loss of p21(WA F1/Cip1) expression and with a monosomy of chromosome 17 in two cases. Homo zygous deletion of the p16(INK4A)/p14(ARF) gene was detected in four (21%) cases, three with codeletion of the p15(INK4B) gene and with chromosome 9 a bnormalities. In all of these cases, expression of the implicated genes was absent. Hypermethylation of the p16(INK4A) and p15(INK4B) genes was detect ed in two (10%) and three (16%) cases, respectively, and was correlated wit h a low level of gene expression. Neither cyclin D1, nor MDM2 and CDK4 ampl ification was observed. Kaplan-Meier analysis showed that patients with tum ors carrying homozygous deletion of the 9p21 locus, or point mutations of t he p53 gene, had poorer outcomes than those without these molecular alterat ions (p = 0.005). in conclusion, 58% (11 of 19) of the analyzed patients sh owed genetic or epigenetic alterations in either the 9p21 locus or p53 tumo r suppressor genes, defining a subgroup of patients with poor clinical outc ome. This fact points to an important role of the G(1)/S cell cycle checkpo int dysregulation in the pathogenesis of EFT.