Koike et al. (2004) Comparison of methylation-specific polymerase chain reaction (MSP) with reverse transcriptase-polymerase chain reaction (RT-PCR) in peripheral blood of gastric cancer patients. J Surg Oncol 87: 182–186

Successful treatment in gastric cancer is limited by the late detection of tumors. A recent paper by Koike and colleagues compares two PCR-based screening methods for early detection.

Preoperative blood samples were obtained from 41 gastric cancer patients and 10 healthy volunteers. Samples were subjected to two assays: CEA-specific nested RT-PCR, in which a positive result indicates that circulating tumor cells are present in the original sample; and the MSP assay, which differentiates between methylated and unmethylated promoter regions of the p16, E-cadherin and RAR[beta] genes. Hypermethylation is a marker of downregulation or silencing of tumor suppressor genes, and hence indicates that tumor DNA fragments are present.

The CEA-specific RT-PCR assay gave a positive result in 10 (24%) patients and the detection rate was higher in stage III or IV disease than in stages I or II (P < 0.01). The MSP assay detected aberrant methylation of p16 in 9 (22%) patients, E-cadherin in 9 (22%) patients and RAR[beta] in 6 (15%) patients. Overall, 18 (44%) patients showed aberrant methylation of the promoter region of at least one of the genes tested, and a positive result correlated with venous invasion (P < 0.05).

While the overall detection rate of the MSP assay was higher than that for CEA-specific RT-PCR, Koike et al. suggest that both assays will be useful for identifying patients requiring more intensive screening and treatment.