Thymidylate synthase protein expression: Association with response to neoadjuvant chemotherapy and resection for locally advanced gastric and gastroesophageal adenocarcinoma.

PURPOSE: A phase II study of neoadjuvant fluorouracil, leucovorin, and interferon alpha-2a was conducted to determine the feasibility of this regimen's use and the response rates in patients undergoing resection for locally advanced gastric or gastroesophageal adenocarcinoma. Also, tumor protein expression of free, total, or bound thymidylate synthase before and after initial exposure to fluorouracil was quantitated to determine if thymidylate synthase expression is associated with response in this treatment setting. PATIENTS AND METHODS: Twenty-two patients with T3-4N0-2M0 gastric or gastroesophageal adenocarcinoma were treated with three cycles of neoadjuvant fluorouracil (370 mg/m2 intravenously on days 2 through 6), leucovorin (500 mg/m2 intravenously on days 2 through 6), and interferon alpha-2a (5x106 U/m2 subcutaneously days 1 through 7), followed by resection and three cycles of consolidation therapy. Endoscopic tumor biopsies were done in 13 patients before therapy and during cycle 2 of the 5-fluorouracil/leucovorin/interferon regimen, and total thymidylate synthase, free thymidylate synthase, bound thymidylate synthase, and percent complexed thymidylate synthase were quantitated by Western blot. Tumor protein expression was evaluated for its association with response to neoadjuvant therapy and patient survival. RESULTS: Eight of 21 (38%) evaluable patients had a partial response, and another 5 of 21 (24%) had a minor response (25% to 49% tumor reduction) after three cycles of neoadjuvant fluorouracil/leucovorin/interferon. The pretreatment total thymidylate synthase level was significantly higher in five nonresponders than in eight responders. After exposure to fluorouracil, levels of free thymidylate synthase were significantly lower and the percent bound thymidylate synthase was higher in responders than in nonresponders. The median potential follow-up period is 24 months, and 11 of 21 patients have died from disease. CONCLUSIONS: These preliminary results indicate that a response to neoadjuvant fluorouracil-based therapy may be associated with decreased levels of total thymidylate synthase before therapy and free thymidylate synthase after exposure to fluorouracil in patients with locally advanced gastric cancer. Quantification of thymidylate synthase protein expression before and after exposure to fluorouracil may provide a method to select patients for fluorouracil therapy in the neoadjuvant, adjuvant, or advanced-disease setting based upon the fundamental sensitivity of the tumor.