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LBA3506 Background: Patients (pts) with initially unresectable CRLM may qualify for curative-intent local therapy after downsizing by induction systemic therapy. The CAIRO5 study aims to find the optimal induction regimen. We present the results of pts with right-sided and/or RAS/ BRAFV600E mutated primary tumors. Accrual in pts with left-sided and RAS/ BRAFV600E wildtype tumors is ongoing. Methods: Pts were randomized between FOLFOX or FOLFIRI + bevacizumab (B) (arm A) and FOLFOXIRI-B (arm B), in both arms up to 12 cycles and followed by 5FU/LV/B maintenance. Prior systemic or local therapy for metastases was not allowed. Unresectability of CRLM at baseline was assessed by an online liver expert panel of surgeons and radiologists based on predefined criteria, and resectability every 2 months thereafter based on panel majority vote. The primary endpoint was progression-free survival (PFS). Secondary endpoints were R0/1 resection, overall survival, overall response rate (ORR), toxicity, pathologic response, postoperative morbidity and correlation of panel evaluations with outcome. Pts were stratified by potentially resectable vs permanently unresectable CRLM, serum LDH (normal/abnormal), BRAFV600E mutation, sidedness, choice of irinotecan vs oxaliplatin and institute. To detect a hazard ratio (HR) of 0.70 for PFS with 80% power and a 2-sided log-rank test at 5%, 257 events were required, assuming a median PFS of 8.7 months for arm A. Results: From December 2014 until March 2021, 294 pts were randomized, 148 in arm A and 146 in arm B in 43 Dutch and 1 Belgian sites. 3 ineligible pts were excluded. Median follow up was 40 months. Pts received a median of 10 vs 9 induction cycles in arm A vs B. Main characteristics were (arm A/B): median age 61/65 years, male 63.9/60.4%, right-sided primary tumor 39.5/41.7%, RAS mutant 85.7/86.1%, BRAFV600E mutant 6.8/8.3%, synchronous disease 86.4/89.6%, prior adjuvant chemotherapy 4.8/4.9%, median number of CRLM 12/12. With 259 events, median PFS in arm A vs B was 9.0 vs 10.6 months (stratified HR 0.74, 95% CI 0.57-0.96, p=0.02). ORR was 32.0% vs 52.1% (p

3562 Background: Decision on optimal treatment strategy for CRLM remains complex because uniform (un)resectability criteria are lacking. We hypothesize that the use of an expert panel can improve the identification of patients with potentially resectable CRLM. The Dutch Colorectal Cancer Group (DCCG) Expert Panel was established in conjunction with the CAIRO5 study (Huiskens J et al. BMC Cancer 2015), a multicenter, randomized, phase-3 trial, investigating optimal systemic induction treatment in patients with initially unresectable CRLM. Here, we present the feasibility of this panel. Methods: The DCCG Expert Panel consists of 13 liver surgeons and 4 radiologists. Consensus was reached on predefined (un)resectability criteria at baseline. An online platform allowed resectability-assessment by 3 surgeons in case of inter-surgeon agreement, and 5 surgeons if they disagreed. CRLM were assessed as 1) resectable 2) potentially resectable, or 3) permanently unresectable. Patients with initially unresectable CRLM were evaluated at baseline and subsequently every 2 months as long as CRLM were considered potentially resectable. Results: Overall, 397 panel evaluations in 183 patients were analyzed. Median time to panel conclusion was 7 days (IQR 5-11 days) and 204 (51%) evaluations showed inter-surgeon disagreement, with major disagreement (resectable versus permanently unresectable) in 24 (14%) and 12 (29%) evaluations after 2 and 4 months of systemic treatment. Ultimately, 84 (79%) patients with resectable CRLM underwent resection and 23 (27%) resections included portal vein embolization or 2-stage procedures. In resectable CRLM with inter-surgeon agreement versus disagreement, R0 resection was achieved in 39 (75%) versus 28 (52%) patients, p = 0.013. Median time to recurrence was similar between resections with panel agreement versus disagreement, 8 versus 6 months, p = 0.447. Conclusions: This study shows the feasibility of a national Liver Expert Panel for prospective resectability assessment of patients with initially unresectable CRLM. High inter-surgeon disagreement supports the use of a panel. We aim to further validate the panel with outcome parameters. Clinical trial information: NCT02162563.

3558Background: The European Organization for Research & Treatment of Cancer & European Society of Surgical Oncology joined forces to build an infrastructure for surgical quality assurance (QA) in ...