Lack of correlation between immunohistochemical expression of E2F-1, thymidylate synthase expression and clinical response to 5-fluorouracil in advanced colorectal cancer

Background: The level of the enzyme thymidylate synthase (TS) is known to inversely correlate with the clinical activity of 5-fluorouracil (FU) in advanced colorectal cancer patients. Since the correlation is not very strong, we have retrospectively analyzed the expression of E2F-1 in tumor samples or metastases from 25 patients with advanced colorectal cancer, homogeneously treated with an FU-based regimen. E2F-1 is a transcription factor regulating the expression of TS along with other crucial DNA synthesis related enzymes. Materials and methods: E2F-1 expression was analyzed by immunohistochemistry using the anti-E2F-1 monoclonal antibody KH95, scoring 2000 cells/case. Expression of TS was evaluated by immunohistochemistry using a rabbit anti-human polyclonal antibody. Results: The level of E2F-1 expression did not correlate with TS expression, although a trend for correlation between E2F-1 level and maximal tumor shrinkage was observed (r = 0.42; P = 0.054). Conclusions: in spite of previous reports demonstrating that E2F-1 quantified by rt-PCR and western blot correlates with TS and could be used as a predictor to select colorectal cancer patients more likely to respond to FU treatment, our data suggest that, under these experimental conditions, immunohistochemistry cannot be used for such selection.