@mjay
To add to Laurie's very complete response, the reason why most oncologists don't test for estrogen levels (and other biomarkers like testosterone, leptin, and inflammatory proteins) is that they change from day to day, even without our ovaries. Apparently, the aromatase enzyme is produced in our extra fat cells, and it converts to estradiol (estrogen). The AI (aromatase inhibitor) which you are taking is designed to block that conversion. These extra (total body fat) fat cells also are responsible for long-term, low grade inflammation in our bodies, and that, too, is linked to a higher risk for breast cancer.