ALDH1A1 and breast cancer: ALDH1A1 upregulates the secretion of granulocyte macrophage-stimulating factor (GM-CSF) by activating the TAK1/NF-κB signaling pathway to increase the enrichment of myeloid-derived suppressor cells (MDSCs) in the tumor microenvironment (TME) of breast cancer, and to inhibit the proliferation and activation of killer T cells [119].