For instance, in breast cancer cells, inhibiting the overexpressed receptor tyrosine kinase‐like orphan receptor 1 (ROR1), which is an upstream regulator of ABCB1 transcription via MAPK/extracellular signal‐regulated kinase (ERK) and p53 pathways, can reduce ABCB1‐mediated drug efflux and resensitize breast cancer cells to doxorubicin.140. This evidence concerns the gene ABCB1 and breast cancer.