June 4, 2024
By Catlin Nalley
New findings showed that vibostolimab coformulated with pembrolizumab (vibo/pembro) led to durable anti-tumor activity and had a manageable safety profile among patients with previously treated, advanced mismatch repair–deficient (dMMR) endometrial cancer.
These results from the cohort B1 of the Phase II KEYVIBE-005 study were recently presented by Carlos Rojas, MD, Executive Director of the Bradford Hill Clinical Research Center in Santiago, Chile, during the 2024 American Society of Clinical Oncology (ASCO) Annual Meeting (Abstract 5502).
This study included adult patients (≥18 years) with advanced dMMR endometrial cancer and progressive disease after one platinum-based chemotherapy regimen (or ≤2 lines if one was administered in the [neo]adjuvant setting). Study participants also had no prior anti–PD-(L)1 therapy, and an ECOG performance status of 0 or 1.
Patients received vibostolimab 200 mg coformulated with pembrolizumab 200 mg Q3W for up to 35 cycles (approximately 2 years). Treatment continued until unacceptable toxicity, disease progression, or withdrawal decision.
The primary endpoint was ORR per RECIST v1.1 by investigator assessment. Secondary endpoints included DOR and PFS per RECIST v1.1 by investigator assessment, overall survival, and safety.
Researchers enrolled 40 patients with a median age of 63 years. Sixty percent of patients had an ECOG performance status of 1. Additionally, 31 patients had previously received one line of therapy in any setting and nine patients had previously received ≥2 lines of therapy in any setting.
The median time from first dose to data cutoff (October 24, 2023) was 17.2 months (range, 7.7-23.4), according to Rojas, who noted that at data cutoff, 23 patients had discontinued treatment and 17 were ongoing. The reasons for discontinuation of treatment were as follows: adverse events (n=11), progressive disease (n=7), clinical progression (n=4), and patient decision to withdraw (n=1).
Rojas reported an ORR of 65 percent. Five patients (13%) had a complete response and 21 (53%) had a partial response. “The median DOR was 13.7 months (95% CI: 12.7-NR) and 75 percent of responders remained in response for ≥12 months based on the Kaplan-Meier method for censored data. Median PFS was 15.0 months (95% CI: 8.1-15.6) and the 12-month PFS rate was 58 percent. Median overall survival was not reached and the 12-month overall survival rate was 82 percent.”
In terms of safety, treatment-related adverse events (AEs) occurred in 38 patients (95%), according to the study authors, who also noted that Grade 3 or 4 treatment-related AEs occurred in 14 patients (35%).
“Nine patients (23%) discontinued treatment due to a treatment-related AE,” the investigators reported. “Any-grade immune-mediated AEs or infusion reactions occurred in 21 patients (53%) and Grade 3 or 4 events occurred in seven patients (18%). No deaths due to treatment-related AEs or immune-mediated AEs or infusion reactions occurred.”
Summarizing his team’s findings, Rojas noted during ASCO, “After 17.2 months of follow-up, this coformulation of vibostolimab plus pembrolizumab demonstrated durable anti-tumor activity and a manageable safety profile in patients with previously treated, advanced dMMR endometrial cancer.
“Overall response rate was 65 percent with 75 percent of respondents experiencing a response for at least 1 year. Median PFS was 15 months and the median overall survival not reached,” he continued. “The addition of vibostolimab to pembrolizumab may improve the efficacy observed with pembrolizumab monotherapy in KEYNOTE-158. These results support further evaluation of this combination in advanced immunotherapy-sensitive tumors.”
Catlin Nalley is a contributing writer.