Although we did not find univariate gene markers in blood associated with HER2 status, the saddlebrown SR module is significantly underexpressed in patients with HER2+ tumors compared to other BC subtypes and controls (fdr = 0.07, S6A Fig) and is enriched for genes involved in B-cell receptor signaling and proliferation (including BLK, CXCR5, CD19, CD79A, CD79B and FCRL5; S4 and S5 Tables). Here, ERBB2 is linked to breast cancer.