Methylation profiles of exocrine and neuroendocrine colorectal carcinomas using methylation-specific multiple ligation-dependent probe amplification.

In this study, we employed Methylation-Specific Multiple Ligation-dependent Probe Amplification (MS-MLPA) to evaluate the methylation status of 34 genes in a series 104 formalin-fixed and paraffin-embedded specimens, including 83 exocrine adenocarcinomas (CRCs) and 21 neuroendocrine cancers (NECs), previously examined for clinico-pathological and molecular features, as well as in 25 colorectal mucosae from 13 CRC patients and from12 non-neoplastic patients. We found higher levels of promoter methylation in normal colonic tissue of CRC-patients with respect to the control group. The CpG Island Methylation Phenotype (CIMP) was observed with similar frequency in exocrine CRCs and in NECs, but different methylation profiles were present in the two tumour types. Microsatellite instability was the marker most strongly associated with CIMP. In both CRCs and NECs, CIMP+/MSI+ tumours represented a homogeneous clinicopathological entity, associated with a very good prognosis compared with the other three classes of cancers. Our results demonstrated that MS-MLPA is a rapid and sensitive method to analyse the methylation status of multiple genes simultaneously and presents innovative aspects that may have important scientific and clinical implications. The use of DNA methylation alterations as a molecular marker system could potentially be a powerful approach to population-based screening for the early detection and for risk assessment of colorectal cancer.