ERBB2 and breast cancer: A phase Ib clinical study (KEYNOTE‐028, NCT02054806) found that pembrolizumab monotherapy showed a modest but sustained overall response in some patients with previously treated, advanced, PD‐L1 positive, ER+/HER2‐breast cancer, with an ORR of 12% (95% CI, 2.5–31.2%), and a median DoR of 12.0 months [142].