Microsatellite instability and the association with plasma homocysteine and thymidylate synthase in colorectal cancer.

The possible associations between microsatellite instability, homocysteine and thymidylate synthase were investigated in tumors and plasma from 130 patients with colorectal cancer. Other analyses included thymidylate synthase and 5,10-methylene-tetrahydrofolate reductase gene polymorphisms, carcinoembryonic antigen, vitamin B12, and folate. Microsatellite instability of tumors was associated with higher levels of plasma homocysteine (p = 0.008) and higher protein expression of thymidylate synthase (p < 0.001). Supplemental analyses ruled out that the finding could be explained by the other analyzed factors. CEA was not associated with neither homocysteine nor microsatellite instability. The data suggests that there is a more pronounced methyl unit deficiency in microsatellite instable tumors.