Pembrolizumab Monotherapy Shows Anti-Tumor Activity in Metastatic Breast Cancer

Strategic Insights -

Researchers from the University of Malaya, in collaboration with Cancer Research Malaysia, have conducted a phase II clinical trial to evaluate the efficacy of pembrolizumab monotherapy in metastatic HER2-negative breast cancer patients with germline APOBEC3B deletion. The study, published in The Lancet Regional Health - Western Pacific, found that pembrolizumab demonstrated anti-tumor activity in a subset of previously treated patients. The research highlights the importance of understanding the genetic factors that influence the response to immunotherapy in breast cancer.

Key Takeaways:

  • The study enrolled 44 patients with metastatic HER2-negative breast cancer, all of whom were women.
  • 64% of the patients had received 2 or more previous lines of therapy for metastatic disease.
  • The primary endpoint was objective response rate (ORR), which was 20% (9/44) in the total population and 25% (3/12) in the PD-L1-positive population.
  • The disease control rate (DCR) for the study was 52% (23/44), indicating that nearly half of the patients experienced stable disease or better.
  • Pembrolizumab monotherapy was well-tolerated, with 1 patient experiencing a grade 3 adverse event.
  • The median progression-free survival (PFS) was 3.1 months, with a 6-month PFS rate of 27%.
  • The median overall survival (OS) was 15.5 months, with a 12-month OS rate of 66%.

Statistics:

  • 44 patients were enrolled in the study.
  • 64% of the patients had received 2 or more previous lines of therapy for metastatic disease.
  • The objective response rate (ORR) was 20% (9/44) in the total population and 25% (3/12) in the PD-L1-positive population.
  • The disease control rate (DCR) for the study was 52% (23/44).
  • The median progression-free survival (PFS) was 3.1 months.
  • The median overall survival (OS) was 15.5 months.

Sources:

  • Pembrolizumab Monotherapy for Previously Treated Metastatic Her2-negative Breast Cancer With Germline Apobec3b Deletion: Results of the Phase Ii Auror Study, The Lancet Regional Health - Western Pacific, 2025;60:101637.
  • NewsRx. Researchers at University of Malaya Report New Data on Breast Cancer (Pembrolizumab Monotherapy for Previously Treated Metastatic Her2-negative Breast Cancer With Germline Apobec3b Deletion: Results of the Phase Ii Auror Study). Immunotherapy Weekly. August 27, 2025; p 959.