Trial results for the Phase 1 study (NCT03396445) investigating boserolimab as monotherapy and in combination with pembrolizumab (Keytruda) in adults with advanced solid tumors were posted on ClinicalTrials.gov on 2025-11-05. The study primarily assessed the safety and pharmacokinetics of boserolimab, revealing dose-dependent pharmacokinetic profiles.
Background
Pembrolizumab (Keytruda) is an established immunotherapy. This study investigated boserolimab, both alone and in combination with pembrolizumab, in adults with advanced solid tumors, including non-small cell lung cancer and triple negative breast neoplasms.
Trial design
The Phase 1 study (NCT03396445) was a completed trial that enrolled 182 adult participants with advanced solid tumors, including non-small cell lung cancer and triple negative breast neoplasms. The study evaluated boserolimab as monotherapy and in combination with pembrolizumab. It also explored boserolimab with pembrolizumab, pemetrexed, and carboplatin in non-squamous non-small cell lung cancer. The primary purpose was to assess the safety and pharmacokinetics of boserolimab.
Key results
The trial reported geometric mean Area Under the Concentration-Time Curve from time 0 to last quantifiable concentration (AUC0-last) for boserolimab across various dose levels and treatment arms. For boserolimab monotherapy (Arm 1), AUC0-last values ranged from 0.761 day*μg/mL (2 mg Q3W) to 918 day*μg/mL (700 mg Q3W). Specifically:
- Boserolimab 2 mg Q3W: 0.761 day*μg/mL (Geometric Coefficient of Variation: 179)
- Boserolimab 7 mg Q3W: 7.61 day*μg/mL (Geometric Coefficient of Variation: NA)
- Boserolimab 20 mg Q3W: 44.4 day*μg/mL (Geometric Coefficient of Variation: 28.6)
- Boserolimab 70 mg Q3W: 150 day*μg/mL (Geometric Coefficient of Variation: 14.2)
- Boserolimab 200 mg Q3W: 469 day*μg/mL (Geometric Coefficient of Variation: 42.9)
- Boserolimab 700 mg Q3W: 918 day*μg/mL (Geometric Coefficient of Variation: 21.4)
- Boserolimab 30 mg Q3W (Endometrial): 44.4 day*μg/mL (Geometric Coefficient of Variation: 51.7)
In combination with pembrolizumab 200 mg Q3W (Arm 2), AUC0-last values for boserolimab were:
- Boserolimab 2 mg Q3W + Pembrolizumab 200 mg Q3W: 0.816 day*μg/mL (Geometric Coefficient of Variation: 20.8)
- Boserolimab 7 mg Q3W + Pembrolizumab 200 mg Q3W: 3.9 day*μg/mL (Geometric Coefficient of Variation: 117)
- Boserolimab 20 mg Q3W + Pembrolizumab 200 mg Q3W: 26.1 day*μg/mL (Geometric Coefficient of Variation: 38.5)
- Boserolimab 70 mg Q3W + Pembrolizumab 200 mg Q3W: 84.5 day*μg/mL (Geometric Coefficient of Variation: 192)
- Boserolimab 200 mg Q3W + Pembrolizumab 200 mg Q3W: 646 day*μg/mL (Geometric Coefficient of Variation: 16.3)
Additionally, analyses on the difference in percentage of participants who experienced a complete response (CR) or partial response (PR) were reported for endometrial cancer cohorts. The difference between Boserolimab 30 mg Q3W + Pembrolizumab 200 mg Q3W and Boserolimab 30 mg Q3W monotherapy was 6.2% (95.0% CI: -21.2 to 32.8). The difference between Boserolimab 30 mg Q6W + Pembrolizumab 400 mg Q6W and Boserolimab 30 mg Q3W monotherapy was -7.1% (95.0% CI: -32.1 to 17.2). The difference between the two combination regimens (Q3W vs Q6W) was 13.3% (95.0% CI: -11.7 to 38.4).
What this means
The pharmacokinetic data from this Phase 1 study provides insights into the exposure of boserolimab when administered alone and in combination with pembrolizumab across various doses. These findings are crucial for understanding the drug's behavior in the body and for guiding future dose selection in subsequent clinical development. The reported differences in CR/PR percentages for endometrial cancer cohorts, while exploratory, do not indicate a clear benefit based on the wide confidence intervals.
Source
The information regarding these trial results was obtained from ClinicalTrials.gov, a public database of clinical studies. The results for study NCT03396445, titled "Study of Boserolimab (MK-5890) as Monotherapy and in Combination With Pembrolizumab (MK-3475) in Adults With Advanced Solid Tumors (MK-5890-001)," were posted on 2025-11-05 on clinicaltrials.gov.