PD-1 expression on TILs in BCBM was identified in 17 cases (23 %), more frequently in older patients (mean age at brain metastasis diagnosis in PD-1+ and PD-1– groups 59 and 51 years, respectively; P = 0.003), and in cases with HER2-amplified primary breast cancer. The gene discussed is ERBB2; the disease is breast carcinoma.