In the high-risk adjuvant or metastatic setting when you initiate patients on ovarian suppression with the plan to start an AI, what protocol do you follow in terms of rechecking estradiol?

This is an area of intense interest, as well as uncertainty. In truth, unless the patient does not have a uterus, (unusual in premenopause) I typically follow clinical menses and have not followed estradiol.

I agree that there are little available data to guide us in this setting. I generally check ultrasensitive estradiol monthly (immediately prior to the GnRHa injection) before starting the AI and then for a few months on the AI therapy. If in the postmenopausal range I will start the AI therapy, and then if consistently suppressed for a few months on the combination I discontinue testing. I have had a number of patients who have not been adequately suppressed by GnRH agonist therapy (mostly but not always patients with obesity), and in those I reconsider what treatment regimen to use.