CXCL12 and breast cancer: Among the CXCL chemokines associated with breast cancer of ER- status (GRO, CXCL5, CXCL6, and CXCL8) and breast cancer metastasis (GRO, CXCL5, CXCL6, CXCL8, and CXCL12) (67, 68), we found a greater than 500-fold increase in GRO chemokines (CXCL1/2/3) present in the TCM harvested from TNBC cells, compared to TCM harvested from ER+ cells.