Evidence for improved pathologic complete response (PCR) rate after preoperative chemoradiotherapy with 5-FU/oxaliplatin (5FU/OX) for rectal cancer

Abstract

3567 Background: The use of preoperative chemoradiotherapy (chemo/RT) with 5-FU for locally advanced rectal cancer has increased dramatically. The addition of oxaliplatin (OX) to preoperative 5-FU may be a more active regimen than 5-FU alone. This retrospective study was undertaken to describe clinical outcomes in patients (pts) with rectal cancer treated with 5FU/OX or 5-FU alone. Methods: Between 11/90 and 4/05, 114 pts with rectal adenocarcinoma underwent preoperative chemo/RT at the University of Pennsylvania. Chemotherapy consisted of 5FU/OX in 36 (32%) pts and 78 (68%) pts received 5-FU. All pts received preoperative RT (median dose 5040 cGy). The two groups were balanced in terms of demographic and tumor related factors including tumor size, stage and distance from the anal verge. Median follow-up from preoperative chemo/RT was 24 months (range 2–125 months). A total of 105 (92%) pts had surgical resections; 61 (58%) with LAR, 44 (42%) with APR. PCR was defined as either no evidence of viable malignant cells in specimen or scattered, isolated malignant cells without gross residual disease. Non-surgical pts were counted as treatment failures. Results: The PCR rate was 36.1% (95% CI 20.4–51.8%) in 5FU/OX pts and 12.8% (95% CI 5.4–20.2%) in 5-FU pts. The probability of observing 13 PCRs in 36 5FU/OX pts if the actual PCR rate was 15% is equal to 0.001. Rates of any grade III/IV toxicity were similar between each regimen (20% 5FU/OX vs. 17% 5FU). Long term outcomes (2yr rate±SE) of local control, freedom from distant failure and progression-free survival in 23 pts who achieved a PCR were: 100%, 94%±6% and 94%±6%, respectively. In 85 pts with gross residual disease, these rates were: 87%±5, 77%±5% and 71%±6%, respectively. Conclusion: In this retrospective study, patients receiving 5FU/OX with radiation had a higher rate of PCR than those receiving 5FU alone. Overall, a PCR may lead to improved long-term outcomes. A prospective randomized trial to test superiority of the 5FU/OX regimen is warranted. [Table: see text]