**11.2 Pembrolizumab**

Pembrolizumab prevents immune-cell deactivation and inhibition by sterically blocking the interaction of PD-1 and its ligands. Pembrolizumab was the first immune checkpoint inhibitor to be approved as a first-line treatment, as well as the first PD-1-targeted therapy. Pembrolizumab a dose of 10 mg/kg was administered every two weeks to patients with previously treated, advanced TNBC in the KEYNOTE-012 trial, which showed efficacy and an adequate safety profile [63]. The overall response rate was 18.5 percent of the 27 patients who were assessed for antitumor activity, with 17.9 weeks an average response time (**Table 3**) [63]. The KEYNOTE-086 trial is presently examining the use of pembrolizumab (200 mg per 3 weeks) in metastatic TNBC (NCT02447003). Cohorts A and B were presented in an oral session at the 2017 ASCO conference [64, 65]. Cohort A comprises of patients with TNBC who had advanced on at least one systemic treatment. Among the 170-patient cohort, 4.7% responded, and 7.6% accomplished disease control for 24 weeks or longer, which included stable disease, partial response, and complete response [66]. In addition, 0.6% showed an absolute response to pembrolizumab monotherapy, and 27% had a decrease in the target lesion size after the first dose. The KEYNOTE-086 trial's Cohort B included metastatic TNBC with PD-L1+ tumors, without having received some systematic treatment previously. 23% of the 52 patients in this cohort showed an objective responses [64]. The use of pembrolizumab as a primary therapy and the inclusion of PD-L1+ tumors as a criterion for inclusion may have contributed to the increased response in cohort B, with only 58 percent of the patients admitted had a cumulative PD-L1 positive composite score of >1 (**Table 3**) [64].
