<qa>  What is the difference between serum and NAF levels?To examine nipple aspirate fluid analysis in lactating women for local concentration of estrogen, prolactin, glucocorticoids, insulin, parity, prior lactation and age. NAF secretors have been reported to have modest increase in breast cancer risk compared to non-secretors . Estrogen levels have been found to be markedly higher in NAF samples than in the serum collected from the same women. Estradiol and estrone concentrations in premenopausal women are 10x and 20x greater in NAF samples than in serum and 50x and 35x greater in post-menopausal women not on HRT. It has been suggested that the disparity between serum and NAF levels may be due to local estrogen production via aromatase and sulfatase. 