Efficacy and safety of PD-1/PD-L1 inhibitors in triple-negative breast cancer: a systematic review and meta-analysis

Objective Triple-negative breast cancer (TNBC) is a subtype of breast cancer with a poor prognosis that seriously threatens women's health. There is still a lack of effective therapeutic targets for TNBC treatment. We conducted a meta-analysis to evaluate the efficacy and safety of programmed cell death protein 1 (PD-1)/programmed death protein ligand 1 (PD-L1) inhibitors in combination with chemotherapy for TNBC patients.Methods We searched PubMed, EMBASE, Cochrane Library, and Web of Science for randomized controlled trials (RCTs) related to PD-1/PD-L1 inhibitors combined with chemotherapy. Literature conforming to the research content was identified according to the inclusion and exclusion criteria. The endpoints of efficacy were pathological complete response (pCR), event-free survival (EFS), progression-free survival (PFS), and overall survival (OS). Safety outcomes included adverse events (AEs) of any grade, AEs of grade ≥3, serious AEs, and the incidence of various AEs. We obtained odds ratios (OR), hazard ratio (HR), and 95% confidence interval (CI) for the included studies. Data analysis was performed using Review Manager software (version 5.3).Results A total of 4468 patients from eight RCTs were analyzed. PD-1/PD-L1 inhibitors in combination with chemotherapy significantly improved pCR (OR, 1.59; 95% CI, 1.28 − 1.98, p < 0.0001), EFS (HR, 0.66; 95% CI, 0.48 − 0.91, p = 0.01), and OS (HR, 0.72; 95% CI, 0.52 − 0.99, p = 0.05) in patients with TNBC compared to chemotherapy alone or placebo in combination with chemotherapy. Furthermore, we found that the pCR rate was almost identical in the PD-L1 positive group (OR, 1.65; 95% CI, 1.26 − 2.16, p = 0.0002) and the PD-L1 negative group (OR, 1.56; 95% CI, 1.04 − 2.33, p = 0.03). Among patients with advanced-stage TNBC, PFS (HR, 0.82; 95% CI, 0.74 − 0.90, p < 0.0001) was longer in the combination therapy group than in the chemotherapy group. There were no statistically significant differences between the experimental and control groups in OS (HR, 1.03; 95% CI, 0.74 − 1.42, p = 0.87). In terms of safety, we found that the combination therapy group had a significantly higher incidence of hyperthyroidism in patients with early and advanced TNBC (OR, 5.76; 95% CI, 2.38 − 13.95, p = 0.0001) (OR, 7.86; 95% CI, 2.65 − 23.29, p = 0.0002).Conclusions The combination of PD-1/PD-L1 inhibitors and chemotherapy could improve the survival and prognosis of patients with early and advanced TNBC. Combination treatment may be harmful to the thyroid; therefore, active surveillance and regular follow-up are necessary during treatment.