Addition of immunotherapy to chemotherapy for metastatic triple-negative breast cancer: A systematic review and meta-analysis of randomized clinical trials

Background: One of the front treatment regimens used for metastatic triple-negative breast cancer (mTNBC) is treatment with programmed death-1 (PD-1) or programmed death ligand-1 (PD-L1) blockade combine with chemotherapy. However, the results of such studies have been controversial. Methods: A systematic searched of PubMed, Embase, Cochrane Library, and the proceedings of the last 5 years of several meetings until February 18, 2021. The primary endpoint was the progression-free survival (PFS) of PD L1-positive patients treated with PD1/PD-L1 blockade plus chemotherapy compare with chemotherapy. Results: Overall, 4 studies that included a total of 3007 mTNBC patients were analyzed in this meta-analysis. PFS was significantly improved in the PD1/PD-L1 blockade plus chemotherapy group compared with the chemotherapy group in PD-L1-positive mTNBC patients (hazard ratios, (HR), 0.69; 95% CI, 0.59-0.80; P < .001), also in intention-to-treat (ITT) population (HR, 0.82; 95% CI, 0.74-0.90; P < .001). However, no significant benefit in overall survival (OS) was observed regardless of PD-L1 status or ITT population. The immunotherapy plus chemotherapy has higher adverse events (AEs) compared with chemotherapy (all AEs, Odds ratios (ORs), 2.33; 95% CI, 1.50-3.62; P < .001; grade 3-5 AEs, OR, 1.27; 95% CI, 1.04-1.55; P = .019). Conclusions: This meta-analysis showed that the addition of PD1/PD-L1 blockade to chemotherapy improved PFS in PD-L1 positive mTNBC patients, also in the ITT population. However, no significant benefit in OS was observed in patients of PD-L1 positive or in the ITT population after adding PD1/PD-L1 blockade. We found a higher rate of AEs with the addition of PD1/PD-L1 blockers to chemotherapy.