Significado clínico y biológico de la heterogeneidad intratumoral de la expresión de la proteína PTEN y de las alteraciones moleculares del gen PTEN en glioblastomas

Résumé

Introduction: Glioblastomas display marked phenotypic and molecular heterogeneity. The expression of the PTEN protein in glioblastomas also shows great intratumor heterogeneity, but the significance of this heterogeneity has so far received little attention. Methodology: We conducted a comparative study on paraffin and frozen samples from sixty glioblastomas. Based on PTEN immunostaining, paraffin glioblastomas were divided into positive (homogeneous staining) and both positive and negative (heterogeneous staining) tumors. DNA was extracted from manually microdissected samples from representative areas, and from frozen samples taken randomly from the same tumors. Loss of heterozygocity (LOH) of 10q23, hypermethylation status of the PTEN promoter and mutations of PTEN gene were studied, and the molecular findings were correlated with overall survival. Results: PTEN protein was present heterogeneously in 42 cases and homogeneously in 18 cases. In homogeneous glioblastomas, no correlation was found between PTEN protein expression and the LOH of the gene. Surprisingly, in the heterogeneous glioblastomas, LOH was found significantly more frequently (p<0.001) in PTEN-positive areas (81%) than in PTEN-negative ones (35.7%). In general, molecular results of frozen tissue were representative of the tumor. Only two cases of methylation of the PTEN promoter were identified. Thirteen cases with missense mutations were observed, all of them in the heterogeneous glioblastomas. A significant difference was found for overall survival for LOH 10q23 status (p=0.002) and for homogeneous vs heterogeneous tumors (p=0.014). Conclusion: The more relevant accepted gene mechanisms of inactivation of PTEN do not explain the heterogeneity of the expression of PTEN protein. Heterogeneity of PTEN expression and LOH of 10q23 are independent prognostic factors. Both factors are additive, so that patients with heterogeneous glioblastomas and LOH of 10q23 have the poorest prognosis.