The only study that stratified HER2+ tumors by hormone receptor status found that CD8+ tumor infiltrate was associated with RFS (p = 0.041) (p = 0.064, HR 0.75 % CI 0.51–1.11 n = 227) in hormone receptor negative HER2+ breast cancer but not hormone receptor positive HER2+ breast cancer [15]. Here, ERBB2 is linked to breast cancer.