CYP27B1 and breast cancer: Another limitation of the study is that we did not investigate candidate gene variants in other genes of the vitamin D pathway, such as those encoding vitamin D binding protein (DBP) or enzymes involved in vitamin D activation and degradation (CYP2R1, CYP27B1, CYP27A1, and CYP24A1) [54,55], which could also be associated with breast cancer risk.