590PIMPACT OF PREOPERATIVE CHEMOTHERAPY AFTER NEOADJUVANT CHEMORADIATION ON TUMOR DOWN STAGING IN PATIENTS WITH LOCALLY ADVANCED RECTAL CANCER: A RETROSPECTIVE STUDY

Abstract Aim: In this study, we compared two groups of patients: Group 1 was treated with neoadjuvant chemoradiotherapy (CRT) as standard therapy followed surgery 8 weeks period and Group 2 received both neoadjuvant CRT and preoperative chemotherapy (CT) during waiting 8 weeks period before surgery. We investigated the impact of using preoperative 5FU-based CT after neoadjuvant CRT on tumor size and nodal down staging up until surgery for rectal cancer with standardized total mesorectal excision. Methods: Of 132 patients with rectal cancer, 70 patients with radiologically T3-T4 and/or node positive disease were selected. ECOG performance status was ≤ 1 in all patients. Surgery was planned for 8 weeks after the end of CRT. Twenty patients (28.5%) received mFOLFOX-6 -at least 2 cycles- as preoperative CT until surgery after neoadjuvant CRT (Group 2). All patients were assessed by MRI and pathologic staging. All analyses were performed by using SPSS 17.0. In order to determine the clinicopathological parameters affected the tumor size (T) and nodal (N) down staging, logistic regression model was used. Results: Median age was 62 years; 44 (62.9%) were male. Of 70 patients, 55 (78.6%) patients had T3, 15 (21.4%) patients had T4. Of these, 28(40%) patients had N0 (18 had T3, 10 had T4), 42(60%) patients had N1 and N2. Twenty five patients (35.7%) had T downtaging and 29 (41.4%) had N down staging. The rate of T down staging was 26% (13pts) and 60% (12pts) in groups 1 and 2, respectively (p = 0.007). For patients receiving preoperative CT, N down staging rate was higher than the patients not receiving (55% vs. 36%, respectively). In logistic regression analysis, receiving preoperative CT (p = 0.01), higher level of LDH (p = 0.03) and perineural invasion (p = 0.06) affected T down staging rate. In group 2, 18 (90%) had no disease recurrences, but 21(42%) patients had disease recurrences in group 1. Preoperative mFOLFOX-6 was well tolerated until surgery. Also, there were no significant differences in toxicity or surgical complications in both groups. Conclusions: Our data suggest that using preoperative CT after neoadjuvant CRT is feasible and associated with an increased rate of T down staging in patients with locally advanced rectal cancer without any increase in surgical complications. This observation needs to be confirmed in larger prospective randomized studies. Disclosure: All authors have declared no conflicts of interest.