Trial results for Pembrolizumab (Keytruda) in combination with investigational agents and chemotherapy for extensive-stage small cell lung cancer (ES-SCLC) were posted on 2026-07-01. The PHASE2 study, KEYNOTE-B99, reported an Objective Response Rate (ORR) of up to 73.7% for one of the combination arms.
Background
Pembrolizumab is an immunotherapy agent. This PHASE2 study, KEYNOTE-B99, investigated its use with investigational agents and chemotherapy as a first-line treatment for participants with extensive-stage small cell lung cancer (ES-SCLC).
Trial design
The study, identified as NCT04924101 (MK-3475-B99/ KEYNOTE-B99), was a PHASE2 trial that was COMPLETED. It enrolled 126 participants with Small Cell Lung Cancer, specifically extensive-stage. The trial evaluated pembrolizumab in combination with etoposide/platinum chemotherapy and one of three investigational agents: MK-4830, boserolimab (MK-5890), or lenvatinib (MK-7902). The study's purpose was to evaluate these combinations as first-line treatment, with no formal hypothesis testing planned.
Key results
Results for Objective Response Rate (ORR) as assessed by Blinded Independent Central Review (BICR) per Response Evaluation Criteria in Solid Tumors Version 1.1 (RECIST 1.1) were as follows:
- For the Pembrolizumab + MK-4830 + Chemotherapy arm, ORR was 65.1 Percentage of participants.
- For the Pembrolizumab + Boserolimab + Chemotherapy arm, ORR was 73.2 Percentage of participants.
- For the Pembrolizumab + Lenvatinib + Chemotherapy arm, ORR was 73.7 Percentage of participants.
The Six-Month Progression-Free Survival (PFS) Rate as assessed by BICR per RECIST 1.1 showed:
- 45.2 Percentage of Participants for Pembrolizumab + MK-4830 + Chemotherapy.
- 40.4 Percentage of Participants for Pembrolizumab + Boserolimab + Chemotherapy.
- 55.9 Percentage of Participants for Pembrolizumab + Lenvatinib + Chemotherapy.
Median Duration of Response (DOR) as assessed by BICR per RECIST 1.1 was:
- 6.1 Months for Pembrolizumab + MK-4830 + Chemotherapy.
- 4.7 Months for Pembrolizumab + Boserolimab + Chemotherapy.
- 7.0 Months for Pembrolizumab + Lenvatinib + Chemotherapy.
Median Progression-Free Survival (PFS) as assessed by BICR per RECIST 1.1 was:
- 5.5 Months for Pembrolizumab + MK-4830 + Chemotherapy.
- 5.6 Months for Pembrolizumab + Boserolimab + Chemotherapy.
- 7.5 Months for Pembrolizumab + Lenvatinib + Chemotherapy.
What this means
The PHASE2 KEYNOTE-B99 trial explored various combinations of pembrolizumab with investigational agents and chemotherapy for first-line treatment of ES-SCLC. The results indicate that all three combinations demonstrated notable objective response rates and progression-free survival outcomes. Specifically, the combination of pembrolizumab, lenvatinib, and chemotherapy showed the highest Objective Response Rate at 73.7% and the longest median Progression-Free Survival at 7.5 months among the evaluated arms. These findings suggest potential efficacy for these combinations in this challenging cancer setting, warranting further investigation in larger trials.
Source
These trial results were posted on ClinicalTrials.gov on 2026-07-01. The full details of the study, NCT04924101, are available on clinicaltrials.gov.