The involvement of CYP2W1 in the metabolism and oxidation of estrogen [33], along with the strong association of cytoplasmic CYP2S1 and nuclear CYP2W1 protein with ER‐positive cancers (Tables 1 and 2), suggests that these enzymes may be important as prognostic markers in ER‐positive disease. This evidence concerns the gene CYP2W1 and cancer.