Resectability, conversion and resections rates, and outcomes in RAS&BRAF wildtype (wt), RAS mutant (mt) and BRAFmt metastatic colorectal cancer (mCRC) subgroups in the prospective Finnish RAXO-study

3532 Background: Outcomes of metastasectomy varies with RAS and BRAF-status, but the effect on resectability, conversion and resection rates has not been extensively studied. Methods: The prospective Finnish RAXO study (NCT01531621) included 1086 patients 2011-2018 (Osterlund et al TLRHE 2021, Isoniemi et al BJS 2021) of which 906 were included in this secondary endpoint analysis. Excluded had missing KRAS/ NRAS/ BRAF-V600E test, were untreatable or had an atypical BRAF mutation. We studied repeated centralized resectability assessment, conversion and resectability rates in mCRC, and overall survival (OS) after resection and/or local ablative therapy (LAT) and systemic therapy. Results: Included were 289 RAS& BRAFwt, 529 RASmt (overrepresented) and 88 BRAFmt, with median age 65.8/66.1/66.9 years. Demographics per RAS& BRAFwt, RASmt and BRAFmt showed significant differences in male proportion (68/61/39%), ECOG PS 2-3 groups (16/14/25%), primary tumour location (right colon 16/30/69%, left colon 47/34/17%, rectum 38/36/14%), but not for Charlson comorbidity index, BMI, resection of primary, synchronous presentation or adjuvant therapy (Bonferroni corrected Chi-square). Metastatic profile was different for liver (78/74/61% per RAS& BRAFwt, RASmt and BRAFmt), lung (24/35/28%) and peritoneal (15/15/32%) metastases, but not for lymph nodes or other sites, nor for number of metastatic sites (1 in 53/54/52%). Upfront resectability rates were different with 32/29/15% for RAS& BRAFwt, RASmt and BRAFmt, respectively, as were conversion rates with 16/13/7%, and resection/LAT rates with 45/37/17%, respectively. Kaplan-Meier median OS estimate in R0/1/2-resected and/or LAT group (n = 342) was 83/69/30 months for RAS& BRAFwt, RASmt and BRAFmt groups, respectively and 5-year OS-rates 67/60/24%, with Cox HR ref/1.53 (95% CI 1.04-2.25)/3.11 (1.49-6.49). In the “systemic therapy only” (n = 564) OS was 29/21/15 months and 5-year OS-rates 11/6/2% respectively, with HR ref/1.43 (1.15-1.76)/2.34 (1.73-3.17). Resection/LAT patients had improved OS over “systemic therapy only” patients in all subgroups, HR 5.74 (3.90-8.44)/5.06 (3.92-6.55)/2.89 (1.43-5.86). Conclusions: There were significant differences in resectability, conversion and resection/LAT rates according to RAS& BRAFwt, RASmt and BRAFmt status. OS was also significantly longer for RAS& BRAFwt versus either mutant. Resected/LAT had better OS than “systemic therapy alone” patients in all subgroups. Clinical trial information: NCT01531621.