Repeat sequential oxaliplatin-based chemotherapy (FLOX) and nivolumab versus FLOX alone as first-line treatment of microsatellite-stable (MSS) metastatic colorectal cancer (mCRC): Initial results from the randomized METIMMOX study.

3556 Background: Immune checkpoint blockade (ICB) has revolutionized patient outcome for the small mCRC subgroup with highly immunogenic disease. The majority of mCRC cases, however, are MSS without innate ICB susceptibility. In our ongoing METIMMOX study, we hypothesize that MSS mCRC can be transformed into an immunogenic condition by short-course oxaliplatin-based therapy (FLOX), enabling patients with unresectable, previously untreated metastases to obtain durable disease control when adding ICB therapy. Here we present the protocol-planned interim analysis. Methods: Eligibility criteria include infradiaphragmatic metastasis and C-reactive protein < 60 mg/L. At analysis 15 January 2021, 54 patients stratified according to primary tumor sidedness and mutational status and evaluable for the primary end point (progression-free survival; PFS) had been randomly assigned to a standard-of-care schedule of 8 FLOX cycles Q2W (control arm) or repeat sequential 2 FLOX cycles and 2 nivolumab cycles (240 mg Q2W) to a total of 8 cycles (experimental arm), for both arms before treatment break until disease progression and reintroduction of a new treatment sequence. Radiologic response assessment is every 8 weeks. Safety, tolerability, objective response rate, and duration of response are among secondary end points. Results: At median follow-up of 6.4 (range, 0.5-20) months, patients were well balanced between the treatment arms with regard to the predefined strata and single-organ or multiple-organ metastases. Median PFS for the entire groups of control and experimental arm patients was 5.6 (range, 0.5-15; n = 26) and 6.6 (range, 0.5-20; n = 28) months, respectively. The number of FLOX-related CTCAE grade 3 or higher adverse events, including 2 deaths after initial FLOX administration, was comparable in the two arms. Twelve immune-related grade 3-4 adverse events (no new safety signals) were recorded. In the experimental arm, 4 (16%) patients, all RAS/BRAF-mutant cases, had experienced complete response and 9 (32%) patients had ongoing objective response at 8 months. The control arm cases had 0 with complete response and 6 (23%) with ongoing objective response at 8 months, 1 of whom had proceeded to curative-intent liver surgery. Conclusions: MSS mCRC patients may hold the opportunity of ICB responsiveness evoked by short-course oxaliplatin-based chemotherapy. The search for predictive biomarkers of ICB responsiveness is ongoing in the specifically designed METIMMOX correlative study program. Clinical trial information: NCT03388190.