1. ¹Department of Pathology, The University of Texas MD Anderson Cancer Center, Houston, TX, USA
2. ²Department of Gastrointestinal Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, USA

Correspondence: Dr A Rashid, MD, PhD, Department of Pathology, Box 85, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030, USA. E-mail: arashid@mdacc.tmc.edu

Received 16 June 2005; Revised 27 July 2005; Accepted 2 August 2005; Published online 7 October 2005.

Abstract

Well-differentiated neuroendocrine tumors including pancreatic endocrine tumors and carcinoid tumors are uncommon neoplasms that have site-specific differences in clinicopathological features, clinical course and genetic alterations. The epigenetic alterations in these tumors are not well characterized. We therefore compared methylation of the RAS-association domain family 1, isoform A (RASSF1A), p14, p16 and O⁶-methyl-guanine methyltransferase genes in neuroendocrine tumors from 47 patients including 16 pancreatic, 15 nonileal and 16 ileal neuroendocrine tumors. Methylation of the RASSF1A gene was present in 57% of tumors, p14 in 49%, p16 in 26% and O⁶-methyl-guanine methyltransferase in 13% of tumors. Ileal neuroendocrine tumors lacked methylation of O⁶-methyl-guanine methyltransferase gene (P=0.04). RASSF1A methylation was associated with histopathologic type of tumors (P=0.03) and lymph node metastasis (P=0.004), and p16 methylation with older patient age (P=0.002) and liver metastasis (P=0.04). Two or more genes were methylated in 53% of tumors, one gene was methylated in 30% of tumors, and all four genes were unmethylated in 17% of tumors. Methylation of one or more gene was associated with older age of patients (P=0.01), and methylation of two or more genes was associated with liver metastasis (P=0.044). Our study shows that in neuroendocrine tumors epigenetic alterations vary by tumor subsite and clinicopathologic features, including age of onset, histopatholoic type and metastasis status.