First, I do not usually check estradiol levels in my patients on an aromatase inhibitor, in part because many of the available estradiol assays are not very accurate, and because the AIs are so effective at blocking estrogen production. However, now that you have this value, the first thing I would ...

If the patient was premenopausal at the time of diagnosis but became amenorrheic after chemo, I assume they are still premenopausal and do baseline estradiol and start on tamoxifen. I follow estradiol levels every 6 months for 1.5 years or so and if still postmenopausal range, switch to AI.

I have seen a few patients progress when they were placed on an adjuvant AI assuming they have undergone menopause (post-chemo). Please remember that even if a woman does not have menstrual periods, she may still have ovarian estrogen production (contraindication for AI therapy). Therefore, check es...