Akt/protein kinase B overexpression as an accurate prognostic marker in adult diffuse astrocytoma.

Abstract

Akt/Protein kinase B (PKB) is a common downstream molecule of Ras signaling essential for cell survival. In an attempt to find a novel prognostic marker of diffuse astrocytoma, we performed an immunohistochemical analysis of Akt/PKB with regard to patient survival and regrowth patterns. Twenty-four adult patients with diffuse astrocytoma were similarly managed without early post-operative radiotherapy and followed up for a median period of 7.5 years. They were analysed by immunohistochemistry for Akt/PKB expression as well as p53 protein accumulation, epidermal growth factor receptor (EGFR) expression, and MIB-1 labeling index. The prognostic significance of each molecular covariate was tested by multivariate analysis using Cox's proportional hazard model including age, performance status, and extent of surgical resection. Akt/PKB overexpression significantly correlated with both shorter overall survival (OS) and progression-free survival (PFS) (p = 0.0110). All the Akt/PKB-positive patients with post-operative residual tumours experienced tumour recurrences, whereas only a small fraction of the Akt/PKB-negative individuals had recurrences (p = 0.0070). Invasive recurrence into surrounding brain occurred only in the Akt/PKB-overexpressed tumours. In contrast, MIB-1 labeling index correlated only with OS, while p53 protein accumulation correlated only with PFS. The Cox's proportional hazard model identified Akt/PKB overexpression as a significant prognostic factor for shorter PFS (p = 0.0117). These results show that Akt/PKB overexpression would be suggestive of malignant progression and invasive regrowth of diffuse astrocytoma, and it can serve as a novel prognostic marker for this tumour.