Aberrant hypermethylation of tumor suppressor genes in pancreatic endocrine neoplasms.

Abstract

Because histologic features can be unreliable in determining the malignant potential of pancreatic endocrine neoplasms (PENs), we characterized the methylation patterns of PENs to develop a molecular marker system useful for clinical prognosis. Aberrant promoter methylation of tumor suppressor genes is associated with a loss of gene function that can afford selective growth advantages to neoplastic cells. Gene hypermethylation, coupled with sporadic genetic mutations, defines the heterogeneous biology of human neoplasms. Forty-eight well-differentiated PENs were subjected to methylation-specific polymerase chain reaction to detect aberrant methylation associated with 11 candidate tumor suppressor genes (INK4a/p16, APC, O6-MGMT, hMLH1, p73, E-cadherin, RAR-beta, p14ARF, GST-pi, TIMP3, and RASSF1A). Methylation differences among PENs, subdivided according to tumor size, lymph node status, or liver metastasis, were analyzed, and the association of gene methylation with tumor recurrence and patient survival was evaluated. Aberrant hypermethylation of any of the 11 tumor suppressor genes was detected in 87% of the PENs. In decreasing order of frequency, the 5 most commonly methylated genes were: RASSF1A (75%), INK4a/p16 (40%), O6-MGMT (40%), RAR-beta (25%), and hMLH1 (23%). In general, tumors larger than 5 cm and those associated with lymph node or hepatic metastases exhibited a higher frequency of methylation at each promoter site compared with PENs without malignant histologic features. The methylation of specific tumor suppressor genes was an independent predictor of early PEN recurrence and decreased 5-year survival following surgical resection. The accumulation of methylation of multiple tumor suppressor genes was associated with early tumor recurrence and reduced survival among a subpopulation of patients with lymph node-negative PENs. Aberrant methylation of multiple tumor suppressor genes is associated with advanced tumor stage and identifies molecularly distinct PENs with identical histologic characteristics. The methylation status of specific tumor suppressor genes is predictive of PEN behavior.