ERBB2 and breast cancer: Immunotherapy was associated with improved overall survival (HR = 0.27, 95% CI, 0.10 to 0.69) and disease-free survival (HR = 0.41, 95% CI, 0.20-0.82) for luminal A breast cancer, but reduced disease-free survival (HR = 2.21, 95% CI, 1.09-4.48) for the HER2 subtype of breast cancer.