Lee, B. et al. Aberrant methylation of APC, MGMT, RASSF2A, and Wif-1 genes in plasma as biomarker for early detection of colorectal cancer. Clin. Cancer Res. 15, 6185–6191 (2009).

Colorectal cancer is one of the most commonly diagnosed malignancies worldwide. Early detection of the disease could, therefore, have significant clinical benefits for patients. Colorectal cancer develops as part of a multistep process that involves the progressive accumulation of genetic and epigenetic alterations. Aberrant methylation of CpG islands in the promoter region of tumor suppressor genes has been reported in colorectal cancer and several other malignancies. Moreover, the presence of circulating DNA with aberrant methylation of tumor suppressor genes in the plasma of patients with colorectal cancer has been recently reported. Scientists from Korea investigated epigenetic molecular markers in the plasma of patients with colorectal cancer for early detection of the disease.

In a retrospective study, Lee and colleagues investigated the methylation status of 10 genes in fresh-frozen tumor tissue and corresponding plasma samples of 243 patients with stage I and stage II sporadic colorectal cancer, and 64 patients with colorectal adenoma. The researchers used methylation-specific PCR and assessed genes involved in cell cycle regulation (p14 and p16), DNA repair and protection (hMLH1 and MGMT), signal transduction (APC, RARβ2, RASSF2A and Wif-1), apoptosis (DAPK) and chromatin remodeling (HLTF). Inactivating mutations and silencing by hypermethylation of these genes have already been implicated in the pathogenesis of colorectal cancer.

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It is imperative to differentiate age-related methylation and tumor-specific methylation for the early detection of colorectal cancer; therefore, the researchers also analyzed the methylation status in normal colorectal mucosa from the 276 healthy individuals who had undergone colonoscopy (n = 148). Lee and colleagues did not detect aberrant methylation of DAPK, RARβ2 and RASSF2A. In 2–4% of normal colonic mucosal tissue, however, p14, p16, APC, HLTF, MGMT and Wif-1 were found to be methylated. The methylation status of the genes investigated was not correlated with patients' age, but was found to be tumor-specific. The researchers detected 18–74% of methylation of these genes in tumor tissues; more specifically, 18% for p14, 34% for p16, 27% for APC, 34% for DAPK, 32% for HLTF, 21% for hMLH1, 39% for MGMT, 24% for RARβ2, 58% for RASSF2A and 74% for Wif-1.

Moreover, the methylation status of all the genes, except HLTF was found to be an independent predictive factor of colorectal cancer although the sensitivity of detection in plasma was low. In order to increase the sensitivity of detection of DNA methylation in plasma, multigene analysis was performed. The methylation of APC, MGMT, RASSF2A and Wif-1 showed the best sensitivity and specificity as a diagnostic biomarker. Methylation of one or more of these genes was detected in 91% of tumor tissues and in 86% of plasma samples.

The researchers conclude that tumor-specific methylation of APC, MGMT, RASSF2A and Wif-1 might be a valuable biomarker in plasma for the early detection of colorectal cancer.