Simultaneous Quantification of Aromatase Inhibitors and Estrogens in Postmenopausal Breast Cancer Patients

Abstract

Context Currently there are no assays that can simultaneously quantify serum levels of the third generation aromatase inhibitors (AI); letrozole, anastrozole, and exemestane, and the ultralow levels of estrogens in postmenopausal breast cancer patients on AI treatment. Such measurements may be pivotal for the determination of optimal and individualized treatment regimens. We aimed at developing an LC-MS/MS method for simultaneous assessment of letrozole, anastrozole, exemestane and 17-hydroxy-exemestane as well as subpicomolar levels of estradiol and estrone. Methods Internal standards, calibrators, serum samples and quality controls were in fully automated steps transferred to a deepwell plate for a two-step liquid-liquid-extraction. The extracts were reconstituted and analytes were separated chromatographically using two serially coupled columns, then subject to MS/MS in ESI mode. The method was thoroughly validated and is traceable to two accredited estrogen-methods. Results Measurement range for estrone and estradiol was 0.2 – 12 000 pmol/L and 0.8 – 13 000 pmol/L, and covered the expected therapeutic range for the AIs. All analytes had precision ≤ 13 %, and accuracies within 100 ± 8 %. As proof-of-concept, AI and estrogen levels were determined in sera from postmenopausal breast cancer patients under treatment. Conclusions We present here an assay suitable for the simultaneous measurement of serum levels of all third generation AIs and ultralow levels of estrogens, providing a powerful new tool to study drug efficacy and compliance. The method is highly valuable for postmenopausal patients whose pretreatment estradiol levels are below threshold of detection for most routine assays, but still require suppression.

Importance of endocrine treatment adherence and persistence in breast cancer survivorship: a systematic review

“…However, this is a measurement with many potential sources of error. On the other hand, more direct approaches, such as serum measurements of active metabolites, can provide a more objective status, but have yet to be accessible for large-scale studies [ 34 , 60 , 61 ].…”

“…There is a need for tailored, interdisciplinary, long-term follow-up strategies, including identification and treatment of side effects. Moreover, serum detection of tamoxifen and AI metabolites during the whole treatment period would enable identification of non-adherent patients, and allow doctors to adjust treatment to more functional levels to reduce side effects [ 45 , 61 ]. Establishing AET units in oncological/surgical departments to promote cooperation between clinicians, family doctors, oncology nurses, psychiatrists, psychologists, and social workers may help to ensure that patients receive the care that they need to improve adherence [ 58 ].…”

Quantification of multiple steroid hormones in serum and human breast cancer tissue by liquid chromatography-tandem mass spectrometry analysis

“…The sensitivity of our method is adequate for analysis of serum estrogens in pre-menopausal women, but not for all post-menopausal women (usually varying between 0.003 ng/ml to 0.011–0.016 ng/ml). To quantify very low concentrations of serum estrogens in breast cancer patients receiving aromatase inhibitor treatment, MS-methods that are more sensitive and more specific for estrogen analysis have been developed ( 31 , 32 ). Our method is sensitive for analyzing serum androgens in both men and women, but it may not be sensitive enough for measuring tissue androgens when such a small amount of cancer tissue was used.…”

Alternative dosing regimen of exemestane in a randomized presurgical trial: the role of obesity in biomarker modulation

“…Serum concentrations of estradiol, estrone, exemestane, and 17hydroxy-exemestane were determined simultaneously using a highly sensitive, previously described assay 46 . In short, samples were spiked with isotope-labeled internal standard and extracted with hexane: methyl tert-butyl ether and hexane: isopropyl alcohol in an automated procedure using a Hamilton Star robot.…”