CYP19A1 and breast cancer: Although serum levels have been measured for 26-HC and many other oxysterols (non-esterified plus esterified), before and during breast cancer treatment in a small study and were, in fact, found to increase in women after receiving aromatase inhibitor treatment [81], there is clearly a need for a large-scale study measuring both oxysterols and cholestenoic acids in serum/plasma of breast cancer patients, to understand better the involvement of these molecules in the mechanism underlying breast cancer metastases.