Monitoring of estradiol levels in premenopausal women receiving adjuvant abemaciclib and ovarian function suppression

Approximately 15% of women who receive ovarian function suppression (OFS) as adjuvant treatment for high-risk, localized hormone receptor-positive (HR+) breast cancer may have inadequate estradiol suppression which can require therapeutic modification when used in combination with an aromatase inhibitor (AI). We previously reported that abemaciclib may interfere with the estradiol Abbott Alinity chemiluminescent microparticle immunoassay (CMIA) commonly used to monitor estradiol levels and suggested liquid chromatography-mass spectrometry (LC-MS/MS) is preferred in this setting. The aim of this study was to determine discrepancies in estradiol levels using CMIA compared to LC-MS/MS and subsequent treatment changes in a larger patient population.

We conducted a retrospective review of premenopausal women with early-stage HR+ breast cancer at our institution who received adjuvant OFS and abemaciclib with at least 1 CMIA estradiol level drawn during abemaciclib therapy from October 2021 to April 2023.

Of the 22 women who met criteria for review, 20 (90.9%) had CMIA estradiol levels in the premenopausal range, of whom 9 also had estradiol measured by LC-MS/MS. All 9 women receiving OFS and abemaciclib with estradiol measurements by both methods had premenopausal range CMIA estradiol levels and postmenopausal range LC-MS/MS estradiol levels. Of the 20 patients with premenopausal estradiol levels by CMIA estradiol, treatment changes included increased OFS dosage or preparation (n = 7), change from AI to tamoxifen (n = 3), and surgical oophorectomy (n = 7).

Our findings suggest the likely interference of abemaciclib with the Abbott Alinity immunoassay which may lead to unnecessary treatment changes. It is recommended that the LC-MS/MS assay be used when monitoring estradiol levels in patients receiving abemaciclib concurrently with OFS.