Abstract P1-13-09: Sensitive liquid chromatography-tandem mass spectrometry method for serum estradiol and estrone assessment without derivatisation, overcoming cross reactivity with exemestane

Abstract

Abstract Objective Measuring serum estrogen levels in postmenopausal women on oral aromatase inhibitors is important but challenging. Direct immunoassays are the most widely used techniques for measuring serum estradiol (E2) in research and clinical laboratories. Unfortunately, commercially available immunoassays for E2 lack precision and accuracy in the low range (<20 ng/l) and are susceptible to interference. In addition, particularly in exemestane users biochemical monitoring of E2 is problematic because exemestane metabolites cross react in most immunoassays for E2. We developed a sensitive, routinely applicable liquid chromatography-tandem mass spectrometry (LC-MSMS) method for E2 and estrone (E1) quantification in human serum without the need for derivatization or an extended extraction protocol. Materials and methods Serum E2 levels, assessed with LC-MSMS and electrochemiluminescence estradiol assay (ECLIA) on Modular E170 from Roche Diagnostics, of 10 breast cancer patients treated with exemestane were compared. Limit of quantification (LOQ) was 1.3 ng/l for LC-MSMS (coefficient of variation <20% and signal-to-noise ratio > 10, own validation) and 5 pg/ml for ECLIA (Roche, according to manufacturer). Results Patients treated with exemestane showed much higher E2 levels when measured by ECLIA compared to E2 levels determined by LC-MSMS (Table 1). All patients, but one, had E2 values below LOQ when assessed with LC-MSMS whereas ECLIA measurements showed higher levels with a large variety (mean: 16.5 ng/l; range: 7-33 ng/l). Results for E2 via ECLIA and LC-MSMS for patients treated with exemestanePatientE2 LC-MSMS ng/lE2 ECLIA ng/l1<1.3212<1.373<1.3124<1.3335<1.3156<1.3227<1.398<1.32692.51010<1.310 Conclusion E2 levels in exemestane users measured with ECLIA from Roche are overestimated, probably due to cross reactivity of its metabolites. Therefore, this assay can not be used in these patients. Here, we demonstrate that this hurdle can be overcome by assessment of estrogen values with LC-MSMS. Our group was able to develop such a sensitive method, without derivatization. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P1-13-09.