Further studies documented that Cyp2r1 mRNA levels were significantly lower in the mammary glands of BALB/c mice (and in C57BL/6 mice with the SuperMam1 locus) compared to that in the wild-type C57BL/6 mice, suggesting that the local dysregulation of Cyp2r1 may contribute to the development of mammary cancer by decreasing the local supply of vitamin D [44]. Here, CYP2R1 is linked to breast cancer.