The study has a start-up single-arm design consisting of 2 cycles of the Nordic FLOX regimen followed by 2 cycles of nivolumab for a total of 4 individual cycles (8 weeks, or longer if cycles have been delayed) before radiologic response assessment and patient stratification to continued therapy.~Patients who present less than 10% target lesion reduction at the first radiologic response assessment will proceed to standard-of-care treatment at the Clinical Investigator's discretion. Patients will be followed for PFS (from the date of study enrolment).~Patients who present 10% or higher target lesion reduction at the first radiologic response assessment will continue treatment with alternating 2 cycles of the Nordic FLOX regimen and 2 cycles of nivolumab. From the time of stratification, radiologic response assessment will be every 8 weeks. After a total of 12 individual cycles (4 initial cycles followed by 8 continuation cycles; Sequence 1), patients will enter a break that will persist until disease progression, following radiologic assessment every 8 weeks during the break, when therapy is reintroduced and administered for another total of 12 individual cycles (Sequence 2) before a new break. This go-and-stop schedule will be continued until progressive disease on ongoing therapy (defining PFS), intolerable toxicity, withdrawal of consent, or death, whichever occurs first.
Hypothesis: Patients with metastatic colorectal cancer with DNA mismatch repair-proficient (pMMR) function / microsatellite-stable (MSS) phenotype harbor a non-immunogenic disease that can be transformed into an immunogenic condition by short-course oxaliplatin-based therapy, and may achieve durable disease control or even tumor eradication by the addition of immune checkpoint blockade therapy to the standard-of-care oxaliplatin-based treatment.