Background: Levels of the enzyme thymidylate synthase (TS) are of prognostic significance in colorectal cancer. It may be argued that the levels of TS merely reflect the proliferative activity and could be replaced by markers of proliferation.
Materials and methods: We used immunohistochemical approaches to examine the expression of TS, Cyclin A and Ki-67 in morphologically well-defined tumor areas in consecutive slices of rectal cancer, using the antibodies TS 106, NCL-Cyclin A and Mib-1.
Results: There was a linear relationship between Cyclin A- and Ki-67-positive cells (p < 0.0001). There did not seem to be any significant relationship between TS-expression and the frequency of Cyclin A-positive cells (p = 0.1) but a significant correlation was observed between TS-expression and the frequency of Ki-67-positive cells (p = 0.02).
Conclusion: TS, immunohistochemically-detected in rectal cancer cells, is not associated with an accurate assessment of the proliferative stage. The prognostic value of TS determination can only partly be explained by the proliferative activity.