공고 • Jul 06
Agenus Reports Three-Year Landmark Phase 1b Data For Botensilimab Plus Balstilimab In Refractory Microsatellite-Stable Metastatic Colorectal Cancer Without Active Liver Metastases
Agenus announced three-year landmark Phase 1b data from the fully enrolled C-800-01 cohort evaluating botensilimab (BOT), an Fc-enhanced multifunctional anti–CTLA-4 antibody, plus balstilimab (BAL), an anti–PD-1 antibody, in patients with refractory microsatellite-stable (MSS) metastatic colorectal cancer (mCRC) without active liver metastases. BOT+BAL demonstrated clinically meaningful long-term survival in a heavily pretreated patient population with historically limited benefit from conventional immune checkpoint inhibitors and few durable treatment options after progression on standard therapies. With extended follow-up, median overall survival was 21.2 months and the three-year overall survival rate was 33%, with the Kaplan-Meier curve showing a plateau beyond two years. Available later-line standards in refractory MSS mCRC without active liver metastases have historically reported median overall survival of approximately 10–14 months in relevant analyses, reflecting a treatment setting in which few patients have historically remained alive at later landmark timepoints and pivotal studies have generally focused on median survival rather than mature 36-month overall survival outcomes. The survival profile, curve plateau beyond two years, and proportion of patients alive and off systemic anticancer therapy support the durability of benefit observed with BOT+BAL in this fully enrolled 123-patient Phase 1b cohort. With longer follow-up, the dataset now includes 26 confirmed responses; median duration of response was not reached; and 21 patients, or 17%, were alive and off all systemic anticancer therapy at last follow-up, including 13 responders. The Phase 1b (NCT03860272) cohort included 123 patients with MSS mCRC without active liver metastases. Patients had received a median of three prior lines of therapy; 67% had received at least three prior lines, 15% had received prior anti–PD-(L)1 with or without anti–CTLA-4 therapy, and 30% had received at least one later-line regimen of regorafenib, trifluridine/tipiracil with or without bevacizumab, or fruquintinib. Key Efficacy Results: Median overall survival: 21.2 months, with 24-month and 36-month overall survival rates of 41% and 33%, respectively. Confirmed objective response rate: 21%, including three complete responses and 23 partial responses. Median duration of response: not reached; responses ranged from 1.9 months to at least 37.4 months. Disease control rate: 69% at six weeks. Clinical benefit rate: 28% at 24 weeks. Tumor regression: observed in more than 40% of patients. Treatment-free survival: 21 patients or 17%, were alive and off all systemic anticancer therapy, including 13 responders with a subset of patients remaining free from subsequent therapy or death for more than two years. In a post hoc late-line–exposed subgroup of 37 patients who had received at least one prior regimen of regorafenib, trifluridine/tipiracil with or without bevacizumab, or fruquintinib, BOT+BAL showed a confirmed objective response rate of 22%, median overall survival of 16.2 months, and a three-year overall survival rate of 30%. In this subgroup, median duration of response was 16.6 months, disease control rate was 70%, and clinical benefit rate at 24 weeks was 27%. With extended follow-up, no new safety signals were observed and there were no treatment-related deaths. Immune-mediated diarrhea/colitis resolved in 98% of affected patients, with a median time to resolution of 14 days from onset. Treatment-related immune-mediated diarrhea/colitis was the most common immune-mediated adverse event (42%; grade =3, 15%). The selected Phase 3 regimen of BOT 1 mg/kg plus BAL demonstrated improved tolerability, with lower rates of immune-mediated diarrhea/colitis (27%; grade =3, 10%) than the 2 mg/kg regimen. Together, the mature efficacy, treatment-free survival, and extended safety findings support continued evaluation of BOT+BAL in MSS mCRC and provide rationale for the ongoing randomized Phase 3 BATTMAN trial evaluating BOT+BAL in refractory MSS/proficient mismatch repair (pMMR) metastatic colorectal cancer. C-800-01 is a first-in-human Phase 1b clinical trial evaluating botensilimab with or without balstilimab in patients with advanced solid tumors. The MSS mCRC without active liver metastases cohort enrolled 123 patients who received BOT 1 mg/kg or 2 mg/kg every six weeks plus BAL 3 mg/kg every two weeks. The primary endpoint was safety and tolerability. Secondary endpoints included objective response rate, duration of response, disease control rate, and progression-free survival. Exploratory endpoints included overall survival and clinical benefit rate. Botensilimab (BOT) is a human Fc enhanced multifunctional anti-CTLA-4 antibody designed to boost both innate and adaptive anti-tumor immune responses. Its novel design leverages mechanisms of action to extend immunotherapy benefits to “cold” tumors which generally respond poorly to standard of care or are refractory to conventional PD-1/CTLA-4 therapies and investigational therapies. Botensilimab augments immune responses across a wide range of tumor types by priming and activating T cells, downregulating intratumoral regulatory T cells, activating myeloid cells and inducing long-term memory responses. Approximately 1,300 patients have been treated with botensilimab and/or balstilimab in phase 1 and phase 2 clinical trials. Botensilimab alone, or in combination with Agenus’ investigational PD-1 antibody, balstilimab, has shown clinical responses across nine metastatic, late-line cancers. Balstilimab is a novel, fully human monoclonal immunoglobulin G4 (IgG4) designed to block PD-1 (programmed cell death protein 1) from interacting with its ligands PD-L1 and PD-L2. It has been evaluated in more than 900 patients to date and has demonstrated clinical activity and a favorable tolerability profile in several tumor types.