First-line treatment with chemotherapy, bevacizumab, and atezolizumab led to a statistically significant improvement in progression-free survival (PFS) compared with atezolizumab alone in patients with deficient mismatch repair (dMMR) or microsatellite instability-high (MSI-H) metastatic colorectal cancer (mCRC), according to findings from the phase 3 COMMIT study.

Median PFS stretched from just over 5 months with atezolizumab alone to more than 2 years with the triplet combination, which also led to improved overall response and disease control rates.

However, these gains came at a cost of higher toxicity, with no observed difference in overall survival at a median follow-up of about 3.5 years, reported Caio Max Sao Pedro Rocha Lima, MD, MS, at the ASCO Gastrointestinal Cancers Symposium 2026 press briefing.

Additional work is needed to pinpoint which patients with dMMR or MSI-H mCRC would benefit the most from the intensified regimen, cautioned Rocha Lima, medical oncologist at Atrium Health Wake Forest Baptist Medical Center in Winston-Salem, North Carolina.

With this triplet, “we have seen excellent response rates, tumor shrinkage, and the disease control rate is quite impressive,” noted Vishwanath Sathyanarayanan, MD, ASCO expert in gastrointestinal cancers at Apollo Hospitals, Bangalore, India.

In his view, this triplet combination “definitely holds promise” and may be a “game changer” for the first-line treatment of this subtype of mCRC but agreed that patient selection will be critical given the increased rates of serious side effects and the lack of an overall survival benefit observed so far.

Triplet Benefit, but at a Cost

Recent estimates indicate that 20%-25% of CRCs are diagnosed at a metastatic stage, and about 4%-7% of those tumors harbor dMMR or MSI-H alterations. Immune checkpoint inhibitors have become the standard first-line approach for this subgroup, after KEYNOTE-177 showed that pembrolizumab doubled PFS compared with chemotherapy.

Still, nearly half of patients experience disease progression within a year on single-agent immunotherapy, underscoring the need for more effective strategies, Rocha Lima said. The COMMIT trial tested whether intensifying treatment upfront could improve outcomes.

A total of 102 previously untreated patients with dMMR or MSI-H mCRC were randomly assigned to atezolizumab alone (n = 41) or a modified FOLFOX6 regimen (leucovorin, 5-fluorouracil, and oxaliplatin) and bevacizumab (n = 41). A third arm with chemotherapy plus bevacizumab (n = 20) was closed early after immunotherapy became the standard of care.

At a median follow-up of 3.5 years, the triplet combination led to a 57% reduced risk for progression compared with atezolizumab alone (hazard ratio [HR], 0.43).

At 1 year, the PFS rate was 67% vs 35% with triplet combination vs atezolizumab monotherapy, and the 2-year PFS rates were 54% vs 32% with triplet therapy vs atezolizumab.

In addition, tumor responses were deeper and more frequent with the triplet, Rocha Lima reported. The overall response rate was 86% vs 46% with triplet vs atezolizumab, and complete radiologic responses occurred in 36% vs 19% with triplet therapy vs atezolizumab, and partial responses were seen in 50% vs 27% of patients, respectively.

The disease control rate at 12 months was 63% vs 32% with triplet vs atezolizumab alone. Only 2.8% vs 32% of patients had disease progression with the triplet group vs the monotherapy group, Rocha Lima noted.

However, overall survival did not differ significantly between the two groups at the time of analysis (HR, 1.04; P = .90).

As expected, toxicity was also substantially higher with the intensified regimen than with atezolizumab monotherapy, Rocha Lima reported, with 73% vs 42% of patients experiencing grade 3-4 adverse events.

Much higher rates of grade 3-4 diarrhea (12% vs 0%), fatigue (5% vs 2.4%), neutropenia (27% vs 0%), sensory neuropathy (2.4% vs 0%), and infection (27% vs 12%) were observed in the triplet group. Four patients died during treatment in the triplet group (10%) vs 1 in the atezolizumab group (2.4%).

“It’s important to emphasize that more research is needed to characterize the subset of patients with dMMR/MSI-H colorectal cancer that would require intensification with chemotherapy plus a PD-1 or PD-L1 inhibitor,” Rocha Lima said.

To that end, the researchers plan to perform correlative biomarker analyses to identify patient subgroups that are most likely to benefit from the intensified regimen. These studies will evaluate tumor and immune microenvironment features, circulating biomarkers, and molecular correlates of response and resistance.

The study was funded by the National Cancer Institute and Genentech. Rocha Lima reported having no disclosures. Sathyanarayanan disclosed receiving honoraria from Alkem Laboratories, AstraZeneca, Glenmark, Intas, Lupin Pharmaceuticals, MSD Oncology, NATCO Pharma, Novartis, Reddy Labs, Takeda, and Zydus Pharmaceuticals.