Efficacy and Safety of Pembrolizumab Monotherapy or Combined Therapy in Patients with Metastatic Triple-negative Breast Cancer: A Systematic Review and Meta-Analysis of Randomised Controlled Trials

Background: Metastatic Triple-negative Breast Cancer (mTNBC) is the most aggressive form of breast cancer, with a greater risk of metastasis and recurrence. Research studies have published in-depth analyses of the advantages and disadvantages of pembrolizumab, and early data from numerous trials suggests that patients with mTNBC have had remarkable outcomes. This meta-analysis compares the data from numerous relevant studies in order to evaluate the safety and efficacy of pembrolizumab monotherapy or combination therapies for mTNBC. Methods: To identify eligible RCTs, a thorough literature search was carried out using electronic databases. CMA software was utilized to perform heterogeneity tests using fixed and random-effects models. Results: According to our pooled data, the median Progression-free Survival (PFS) was 2.66 months, and the median overall survival (OS) was 12.26 months. Furthermore, by comparing efficacy indicators between PD-L1–positive and PD-L1–negative groups, a correlation was found between the overexpression of PD-L1 with OS, PFS, and ORR. Patients with PD-L1-positive tumors had a higher response rate, with an ORR of 21.1%, compared to the patients with PD-L1-negative tumors. The ORR for first-line immunotherapy was higher than that of ≥second-line immunotherapy. In addition, pembrolizumab plus combination treatment resulted in a pooled incidence of immune-related adverse events of 22.7%. Conclusion: A modest response to pembrolizumab monotherapy was detected in the mTNBC patients. Furthermore, a better outcome from pembrolizumab treatment may be predicted by PD-L1-- positive status, non-liver/lung metastases, combination therapy, and first-line immunotherapy. Pembrolizumab, in combination with chemotherapy, may be more beneficial for patients whose tumors are PD-L1 positive.