Agenus has announced the peer-reviewed publication of updated results from the Phase 2 NEST trial, showing deep pathologic responses and no observed colorectal cancer recurrences following neoadjuvant botensilimab (BOT) plus balstilimab (BAL) in patients with resectable colon cancer.
The findings were published in Clinical Cancer Research in a paper titled “Neoadjuvant botensilimab/balstilimab for localized mismatch repair proficient and deficient colon cancer: Results of the NEST phase 2 clinical trial.” The updated analysis includes longer follow-up, circulating tumor DNA (ctDNA) findings, and additional analyses of treatment-related changes in the tumor immune microenvironment.
At the March 31, 2026 data cutoff, no colorectal cancer recurrences had been observed, with a median follow-up of 32.2 months in NEST-1 and 23.5 months in NEST-2.
Deep Responses in pMMR/MSS Colon Cancer
NEST was a single-center, open-label, single-arm Phase 2 study evaluating BOT+BAL before surgery in patients with resectable colorectal cancer. The study included 24 eligible patients with 26 tumors, of which 22 were mismatch repair proficient/microsatellite stable (pMMR/MSS) and four were mismatch repair deficient/microsatellite instability-high (dMMR/MSI-H).
Among the 22 pMMR/MSS tumors, neoadjuvant BOT+BAL resulted in:
- 59% pathologic response rate
- 41% major pathologic response rate, defined as 10% or less viable tumor remaining
- 32% pathologic complete response rate, with no viable tumor identified in the tumor or adjacent lymph nodes at surgery
The findings are particularly notable because pMMR/MSS tumors account for the large majority of early-stage colorectal cancers and have historically shown limited sensitivity to conventional immune checkpoint therapy, particularly in the metastatic setting.
All four dMMR/MSI-H tumors achieved a major pathologic response. Two achieved a pathologic complete response, while the other two demonstrated 98% and 99% tumor regression, respectively.
ctDNA Clearance Before Surgery
The investigators also assessed circulating tumor DNA as a marker of molecular response.
Among patients with detectable ctDNA at baseline and evaluable samples before surgery, 88% cleared ctDNA before resection. ctDNA remained undetectable after surgery in all patients who were evaluated. Importantly, all patients proceeded to their planned surgical resections without treatment-related delays.
No Grade 4 treatment-related adverse events, treatment-related deaths, or study discontinuations were reported.
Analyses of paired tumor samples also showed immune changes among responding tumors, including increased CD8+ T-cell infiltration, reductions in FOXP3+ regulatory T cells, increased CD8+/Treg ratios and changes in the spatial organization of immune cells within the tumor microenvironment.
What Are Botensilimab and Balstilimab?
Botensilimab is an investigational multifunctional, Fc-enhanced anti-CTLA-4 antibody designed to activate both innate and adaptive antitumor immune responses and remodel the tumor microenvironment.
Balstilimab is an investigational anti-PD-1 antibody.
The NEST study evaluated whether combining the two agents before surgery could generate antitumor immune activity while the primary tumor, draining lymph nodes, and surrounding immune microenvironment were still present.
Phase 3 ROBBIN Trial Planned
The findings support the further development of BOT+BAL in earlier-stage colon cancer. Agenus is advancing ROBBIN, a planned global randomized Phase 3 trial that will evaluate neoadjuvant BOT+BAL followed by standard of care versus standard of care alone in previously untreated patients with high-risk Stage II or Stage III MSS colon cancer. The planned primary endpoint is event-free survival.
Meanwhile, the NEST3 trial (NCT07595874) is already recruiting. The multicenter Phase 2 investigator-sponsored study is expected to enroll approximately 100 patients across 11 US sites and will further evaluate neoadjuvant BOT+BAL in advanced resectable colorectal cancer. The first patient was dosed in July 2026.
Pashtoon M. Kasi, MD, MS, originator of the NEST study and principal investigator of NEST3, said the findings provide a strong basis for continuing to investigate neoadjuvant BOT+BAL, particularly in pMMR/MSS disease, where immunotherapy has historically had limited impact.
Read further on OncoDaily: Inside the ROBBIN Phase 3 Strategy: Bringing BOT+BAL Into the Neoadjuvant Setting
