CYP4Z1 and breast cancer: To establish the possible role of orphan CYPs in breast cancer development and/or chemotherapy resistance, Tao Xi et al. [17,25,26] analyzed the synergic expression of CYP4Z1 and pseudogene CYP4Z2P in the regular MCF7 cells, tamoxifen-resistant MCF7-TamR, and MDA-MB-231 cell lines.