Subgroup analysis of the METABRIC dataset according to molecular subtype showed that the immune prognostic index was prognostic for HR+/HER2+, HR−/HER2+, and TNBC (P < 0.05), but only not prognostic for HR+/HER2− (P = 0.24) breast cancer (Supplementary Fig. S2). Here, ERBB2 is linked to breast cancer.