Expression of Thymidylate Synthase in Human Non‐small Cell Lung Cancer

5‐Fluorouracil (5‐FU) has been used worldwide, and the correlation between its effects and thymidylate synthase (TS) expression has been reported in gastrointestinal malignancy. But the significance of TS expression for 5‐FU‐based chemotherapy has rarely been reported in non‐small cell lung cancer (NSCLC). We investigated surgically resected specimens of 23 consecutive patients with previously untreated NSCLC. We used immunohistochemistry and western blot analysis with anti‐TS polyclonal antibody to evaluate the existence of TS, and fluorodeoxyuridine‐5′‐monophosphate (FdUMP) binding assay to evaluate the enzymic activity of TS. We found that 14 samples (60.9%) were positive immunohistochemically, and that the results of immunohistochemistry closely reflected the enzymic activity measured by FdUMP binding assay (ranging from 1.8 to 56.9 pmol/g protein). These results seem to support our experience that 5‐FU and its derivatives are clinically significantly effective as a postoperative adjuvant chemotherapy against NSCLC.