578P - Comparison of Pathological Responses (PR) Observed on Colorectal Cancer Metastases (CRCM) Resected After Different Preoperative Treatments

Abstract

ABSTRACT Background Irinotecan (IR) or oxaliplatin (OX)-based regimens optionally combined with anti-VEGF or anti-EGFR Target Therapies (TT) are used as preoperative treatment for metastatic colorectal patients before resection of CRCM. Best combination remains unclear. The study purpose was to compare PR observed on resected CRCM after different preoperative treatments. Methods 114 patients engaged for CRCM resection after 2005 were included in this retrospective analysis. PR was evaluated on 296 resected CRCM according to the pathological Tumor Regression Grading scale (TRG), grading PR from complete (TRG1) to absent (TRG5). Mean TRG of resected metastasis was compared based on Kruskall-Wallis and Mann-Whitney tests. Cumulative PFS were calculated by Kaplan-Meir method and compared by log-rank test. Results 92/114 patients were preoperatively treated. Mean TRG after OX without TT was better than mean TRG after IR without TT (p = .044). No difference was observed between mean TRG after chemotherapy alone compared to mean TRG after chemotherapy + anti-VEGF (p = .53) or to mean TRG after chemotherapy + anti-EGFR (p = .39). Subgroup analysis revealed that mean TRG after IR + anti-EGFR was better than mean TRG after OX + anti-EGFR (p = .031), and that mean TRG after OX + anti-VEGF was better than mean TRG after IR + anti-VEGF (p = .001). PFS analysis for the 92 preoperatively treated patients revealed that 13 patients with major PR (TRG ≤ 2), had a significantly improved PFS compared to 79 patients with minor or no PR (TRG > 2) (median PFS= 33.7 vs 22.9 month p= .018). Conclusion PR observed on resected CRCM after a preoperative treatment does not seem to be linked to the TT (anti-VEGF or anti-EGFR) but rather to the chemotherapy/TT association with a significant advantage for OX + anti-VEGF or IR + anti-EGFR combinations. Preoperative strategy Patients (n) Metastases (n) TRG mean 95% CI No treatment 22 54 4.33 4.11- 4.55 Chemo alone 38 86 3.19 2.95 - 3.43 OX 28 68 3.16 2.89-3.43 IR 8 11 3.91 3.44-4.38 Other 2 7 ND ND Anti-VEGF + chemo 38 120 3.32 3.10 - 3.54 OX 8 27 2.63 2.18 - 3.08 IR 29 80 3.53 3.27 - 3.78 Other 1 13 ND ND Anti-EGFR + chemo 16 36 2.97 2.50 - 3.44 OX 9 16 3.56 2.98 - 4.15 IR 6 19 2.47 1.77 - 3.18 Other 1 1 ND ND Disclosure All authors have declared no conflicts of interest.