Results from a PHASE1 study (NCT05594043) investigating MK-6598 as monotherapy and in combination with pembrolizumab in advanced solid tumors were posted on 2026-07-15. The trial reported low instances of dose-limiting toxicities (DLTs), with 0 to 2 participants experiencing DLTs across various dose cohorts. This study enrolled a total of 39 participants.

Background

Pembrolizumab (Keytruda) is an established immunotherapy. This study investigated MK-6598, both as a monotherapy and in combination with pembrolizumab, for the treatment of advanced or metastatic solid tumors.

Trial design

The study, identified as NCT05594043, was a PHASE1 trial that enrolled 39 participants with advanced or metastatic solid tumors. The trial assessed MK-6598 as monotherapy and in combination with pembrolizumab (MK-3475). The primary objectives included assessing efficacy and safety, and establishing a preliminary recommended Phase 2 dose (RP2D) for MK-6598.

Key results

Key safety results focused on dose-limiting toxicities (DLTs) and adverse events (AEs). For DLTs, the following counts were reported:

  • 0 participants in the 50 mg MK-6598 monotherapy group.
  • 0 participants in the 125 mg MK-6598 monotherapy group.
  • 0 participants in the 250 mg MK-6598 monotherapy group.
  • 0 participants in the 500 mg MK-6598 monotherapy group.
  • 1 participant in the 50 mg MK-6598 + Pembrolizumab group.
  • 0 participants in the 125 mg MK-6598 + Pembrolizumab group.
  • 2 participants in the 250 mg MK-6598 + Pembrolizumab group.

Regarding participants who experienced at least one AE:

  • 4 participants in the 50 mg MK-6598 monotherapy group.
  • 3 participants in the 125 mg MK-6598 monotherapy group.
  • 3 participants in the 250 mg MK-6598 monotherapy group.
  • 9 participants in the 500 mg MK-6598 monotherapy group.
  • 7 participants in the 50 mg MK-6598 + Pembrolizumab group.

Additionally, several percent changes from baseline were reported at Day 22, calculated as [(Measure at Day 22 - Measure at baseline)/Measure at baseline]*100%. These included values such as -54.28%, 630.7%, -63.28%, -70.36%, -28.61%, and -82.14%.

What this means

The low number of dose-limiting toxicities reported in this PHASE1 study suggests that MK-6598, both as monotherapy and in combination with pembrolizumab, generally demonstrated a tolerable safety profile at the tested doses. This is a crucial finding for early-phase oncology trials, as it helps establish potential dose ranges for further investigation. The reported percent changes from baseline, while diverse, indicate some biological activity, though further context on the specific measurements would be needed for a complete interpretation.

Source

This information was sourced from ClinicalTrials.gov, documenting the results of trial NCT05594043, which were posted on 2026-07-15. The study details are available on clinicaltrials.gov.