Abstract 522: Immunogenic chemotherapy and immune checkpoint inhibition (ICI) in microsatellite-stable (MSS) metastatic colorectal cancer (mCRC): Biomarkers indicative of durable treatment response

Purpose: Cancer immune therapy has revolutionized patient outcome for the small mCRC subgroup with highly immunogenic disease. The majority of mCRC cases, however, are MSS with inherently low susceptibility to immune therapy. In our ongoing METIMMOX study (NCT03388190), MSS-mCRC patients are randomized to oxaliplatin-based immunogenic chemotherapy followed by ICI (experimental study arm) or the oxaliplatin-based standard-of-care (control arm). A subgroup of experimental arm patients has obtained durable major partial or complete responses. Such remarkable outcomes call for biomarkers that may help identifying MSS-mCRC patients who will benefit from such sequential therapy. Experimental procedures: Study enrollment began August 2018. Patients with unresectable, previously untreated MSS-mCRC have been randomized to the Nordic FLOX regimen (standard-of-care) or repeat sequential 2 FLOX cycles and 2 cycles of nivolumab (240 mg Q2W). At analysis October 2020, 48 patients were evaluable for progression-free survival (PFS). Serum collected at baseline and after the first 2 FLOX and 2 nivolumab cycles were analyzed for 42 immune factors with the Luminex multiplex immunoassay. The Significance Analysis for Microarrays method was applied to select the most significant proteins. Diffusion-weighted magnetic resonance imaging (DW-MRI) of the liver was performed at baseline and after the first 2 FLOX cycles. Using a b-value of 1000 s/mm2, the intensity ratio of a representative metastatic lesion relative to normal parenchymal tissue in the liver was calculated at each recording. Results: At this early time of analysis, with median follow-up of 8.6 (range, 1-21) months, median PFS for the entire groups of control and experimental arm patients was identical (6.4 and 6.6 months, respectively). We selected 13 experimental arm patients with long (median 13.6 months) or short (median 5.6 months) PFS for the serum protein analysis and 9 patients with liver DW-MRI. High serum CD40L levels (> median 47.6 ng/ml) at baseline or CD23 levels (> median 15.7 ng/ml) after the first 2 FLOX and 2 nivolumab cycles were both associated with improved PFS (p Conclusions: Three potential response markers in serum or at DW-MRI (one at baseline, one following the induction immunogenic chemotherapy, and one following the subsequent ICI) were identified for MSS-mCRC at this early time of the METIMMOX study conduct. Citation Format: Anne Hansen Ree, Sebastian Meltzer, Kine M. Bakke, Hanne M. Hamre, Christian Kersten, Eva Hofsli, Marianne Gronlie Guren, Halfdan Sorbye, Christin Johansen, Anne Negard, Kathrine Roe Redalen, Kjersti Flatmark. Immunogenic chemotherapy and immune checkpoint inhibition (ICI) in microsatellite-stable (MSS) metastatic colorectal cancer (mCRC): Biomarkers indicative of durable treatment response [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 522.