Role for p16INK4a in progression of gastrointestinal stromal tumors of the stomach: alteration of p16INK4a network members

SummaryGastrointestinal stromal tumors feature a wide spectrum of biologic behavior, ranging from benign to extremely malignant. To determine the role of p16INK4a alteration in progression of gastrointestinal stromal tumors of the stomach, we have investigated protein expression and gene methylation in correlation with clinicopathologic factors and survival. In addition to immunohistochemical analysis of p16INK4a in a series of 95 cases, real-time quantitative methylation specific polymerase chain reaction for p16INK4a and immunostaining for cyclin D1, cyclin E, pRb, DP-1, E2F-1, and Ki-67 were also evaluated in randomly selected samples. The p16INK4a labeling indices ranged from 0% to 74% (median, 21%), demonstrating a significant inverse correlation with size (P = .046). On univariate (P = .003) and multivariate (P = .067) analyses, loss of p16INK4a expression increased the likelihood of a poor tumor-related survival. In addition, size (P = .036) and the mitotic index (P = .005) had independent prognostic influence. The p16INK4a methylation index, which ranged from 0% to 100% (median, 17%), was significantly higher in larger tumors (P < .001) and in high-risk category lesions (P = .001) and inversely correlated with protein expression. Hierarchical cluster analysis based on expression of p16INK4a network members identified 2 clusters in 27 randomly selected tumor samples, containing 11 and 16 tumors each. Former cluster samples demonstrated higher risk category (P = .022), higher p16INK4a methylation (P < .001), and more reduced pRb expression (P < .018). In addition, p16INK4a network members clustered into 2 groups: (1) showing down-regulated p16INK4a protein and up-regulating of both cyclin D1 and DP-1 and (2) down-regulated pRb and up-regulated E2F-1. We conclude that p16INK4a alteration has an important role in progression of gastrointestinal stromal tumors of the stomach. Furthermore, the study provides a possible link between regulation of p16INK4a network members and gastrointestinal stromal tumors.