ACKR1 and triple-negative breast carcinoma: While the previous study identified the subsets characterized by ACKR1, LYVE1, CXCL12 and RGS5 (right, Fig. 6D), M138 is a unique subset of capillary endothelial cells (ECs) characterized by CA4 expression (Fig. 7E) [41, 42] and is present in ER+, Her2+, and triple-negative breast cancer (TNBC) subtypes, with enrichment of cells from TNBC, compared to the pool of all ECs (Fig. 7F; Fisher’s exact test [FET] P = 8.71E-5, Enrichment fold change (EFC) = 1.62).