Relationship between thymidylate synthase (TS) genotype and TS expression: a tissue microarray analysis of colorectal cancers.

Response of colorectal cancers to 5-fluorouracil appears to be influenced by differences in thymidylate synthase (TS) expression. To explore the relationship between TS 5' genotype and expression, we analyzed paired tumor and normal tissue from 87 colorectal cancers by tissue microarray. A trend to an association between TS genotype and expression was observed, but the correlation was weak. Although the 2R homozygote was preferentially associated with TS expression (p<0.03), no relationship was observed for the 3R homozygote (p=1.0). The relationship between 5' TS genotype and TS expression is not simple. For clinical trials incorporating TS status, detection of TS expression in tumors by immunohistochemistry must still remain the benchmark over genotype.