Clinical Trial Results for Pembrolizumab in Triple-Negative Breast Cancer

Overview of Triple-Negative Breast Cancer

A recent randomized phase 3 clinical trial has demonstrated that the combination of pembrolizumab and chemotherapy significantly enhances the pathological complete response in patients with early-stage triple-negative breast cancer (TNBC). TNBC, which accounts for approximately 15% of all breast cancer cases, is characterized by its aggressive nature and elevated rates of early recurrence and mortality. This subtype is termed “triple-negative” due to the absence of the estrogen receptor, progesterone receptor, and HER2 protein, which renders hormone therapy and HER2-targeting treatments, such as Herceptin and Enhertu, ineffective. Consequently, managing TNBC presents substantial challenges.

Standard Treatment and Ongoing Research

Currently, the primary treatment for TNBC involves neoadjuvant chemotherapy, which is administered prior to surgical intervention. In efforts to enhance chemotherapy efficacy, various clinical trials are exploring targeted drug therapies. A recent study published in The New England Journal of Medicine evaluated the impact of adding pembrolizumab to chemotherapy for patients diagnosed with stage II or III TNBC.

Trial Design and Results

The trial included 1,174 newly diagnosed TNBC patients from 21 countries, who were randomly assigned in a 2:1 ratio to receive either pembrolizumab combined with chemotherapy or placebo combined with chemotherapy. Pembrolizumab, a monoclonal antibody, functions by blocking the programmed death ligand 1 (PD-1) receptor, aiming to stimulate anti-tumor activity. Administration of either pembrolizumab or placebo occurred during both the neoadjuvant and adjuvant phases of treatment.

At the time of definitive surgery, results showed a significant difference in pathological complete response rates: 64.8% in the pembrolizumab-chemotherapy group compared to 51.2% in the placebo-chemotherapy group, reflecting an improvement of 13.6%. Follow-up over 15.5 months indicated that disease progression affected 7.4% of patients in the pembrolizumab group versus 11.8% in the placebo cohort.

Adverse Events and Safety Profile

Common adverse events reported in both treatment groups included neutropenia, characterized by a reduction in blood neutrophil levels, and anemia, aligning with typical side effects associated with platinum-based chemotherapy. Notably, fewer treatment-related adverse events were observed in the placebo-chemotherapy group (73%) compared to the pembrolizumab-chemotherapy group (78%).

Conclusion and Future Directions

The findings from this study are promising, indicating that the incorporation of immune checkpoint inhibitors like pembrolizumab into neoadjuvant chemotherapy regimens could lead to a higher rate of pathological complete responses among TNBC patients. Ongoing research aims to further assess the safety profile of pembrolizumab and its effects on the survival outcomes of patients with TNBC.

Written by Albina Babu, MSc

References:

  • Schmid, P., et al. (2020). Pembrolizumab for Early Triple-Negative Breast Cancer. New England Journal of Medicine, 382(9), pp.810-821.
  • Anders, C.K., Zagar, T.M. and Carey, L.A. (2013). The Management of Early-Stage and Metastatic Triple-Negative Breast Cancer: A Review. Hematology/Oncology Clinics, 27(4), pp.737-749.

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