Prospective Phase II Randomized Trial of Postoperative Adjuvant Chemotherapy in Patients With High Risk Colon Cancer

Approximately 75% of all patients with colon carcinoma present at a stage when all gross tumor can be surgically resected. Despite that high resectability rate, about 50% of all colon adenocarcinoma patients die of subsequent metastatic disease not apparent at surgery. These individuals could benefit from adjuvant local or systemic chemotherapy.

Based on the encouraging antitumor activity of 5-FU plus leucovorin(LV) in patients with metastatic colon carcinoma6,7, several investigators reported their results using this combination in the adjuvant setting. Results of an NSABP C-038 suggested that postoperative 5-FU plus leucovorin reduces the risk of colon cancer recurrence by 30% and the associated mortality by 32% compared with MOF(semustine, vincristine, and 5-FU). Recently, investigators from the IMPACT group9 analyzed the role of adjuvant 5-FU plus high dose leucovorin given 5 days every 28 days for a total of six courses versus no treatment in patients with stage II or III colon cancer. The treatment arm showed a significant reduction (by 22%) in mortality (P=0.029) and a 35% reduction in relapse rate (P=0.0001). Preliminary results from other studies have also suggested benefits of 5-FU plus leucovorin as adjuvant treatment of colon cancer10,11,12. Those studies had employed chemotherapy with 5-FU plus leucovorin, although there were differences in duration of treatment and drug dose among those trials, it is striking that all revealed a similar magnitude of benefit for adjuvant chemotherapy with 5-FU and leucovorin in node positive patients. At the present time, both 5-FU plus levamisole and 5-FU plus leucovorin can be considered acceptable adjuvant chemotherapy regimens for patients with node positive disease.

Thymidylate synthase(TS) is a critical therapeutic target for the fluoropyrimidine cytotoxic drugs that are the mainstay of the treatment for patients with advanced colorectal cancer. TS provide the sole de nono source of thymidylate for DNA synthesis. The clinical importance of TS in determining fluoropyrimidine cytotoxicity has been established in both clinical and preclinical study. Increased expression of TS protein due to underlying gene amplification has been described in cell lines selected for drug resistance by exposure to 5-FU.22,23 Several investigators have also demonstrated that intratumoral TS activity are predictive for response to 5-FU.24-26 High TS activity was associated with no response, whereas a low TS activity was associated with good response to 5-FU.