Are there patients with HR+/HER2– metastatic breast cancer for whom you would add pembrolizumab to chemotherapy after progression on endocrine therapy plus a CDK4/6 inhibitor, despite KEYNOTE-B49 results showing improved PFS but no OS benefit?

Pembrolizumab is not FDA-approved for HR+ breast cancer outside tumor-agnostic indications. The NCCN endocrine-refractory HR+/HER2– algorithm (v9.2026) does not list it with chemotherapy; checkpoint inhibitors appear only through the MSI-H and TMB-H biomarker options.

The final KEYNOTE-B49 analysis s...