ESR1 and breast cancer: CXCL1 causes the migration of triple-negative MDA-MB-231 breast cancer cells [40,73,78], MCF-7 cells (ER+PR+HER2−) [78,81], Zr-75-1 cells (ER+PR+HER2+) [81], triple-negative HCC-1937 breast cancer cells, and HER2-positive SKBR3 breast cancer cells (ER−PR−HER2+) [78].