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Abstract
Optimal care for breast cancer patients undergoing aromatase inhibitor (AI) treatment is ensured when estradiol (E2) levels are adequately suppressed. To assess treatment efficacy accurately, it is important to measure the serum E2 levels using a well validated assay method with high sensitivity and specificity. This translates into the urgent need to evaluate various E2 immunoassay kits, which are frequently used in hospital settings to measure E2 serum levels in patients undergoing AI treatment, so clinicians obtain accurate and reliable measurements allowing appropriate clinical decision making. Our objective was to evaluate the performance of different commercially available and commonly used E2 immunoassay kits regarding measurement of E2 levels in the serum of postmenopausal breast cancer patients treated with AIs, in comparison to a highly accurate and reliable mass spectrometry assay. Clinical and demographic data were obtained from 77 postmenopausal breast cancer patients who were treated with an AI. Serum E2 levels were measured by 6 immunoassay methods and by liquid chromatography-tandem mass spectrometry (LC-MS/MS), which served as the standard for comparison. Analysis of E2 by LC-MS/MS showed that 70% of the samples had levels that were <5 pg/ml. Three of the assays carried out with commercial E2 immunoassay kits had poor sensitivities and were not able to detect E2 levels <10 or <20 pg/ml. Although two of the E2 assays using commercial kits demonstrated a better sensitivity (5 pg/ml), the measured E2 values were substantially higher than those obtained by LC-MS/MS. The assay with the sixth commercial E2 kit grossly underestimated the true E2 values. E2 assays carried out with commercial E2 immunoassay kits lack the accuracy to measure the very low serum E2 levels found in patients being treated with AIs. Serum samples from such patients should be sent to laboratories that use a mass spectrometry assay.Electronic supplementary materialThe online version of this article (doi:10.1186/2193-1801-2-5) contains supplementary material, which is available to authorized users.
Highlights
Hormone suppression in postmenopausal women with estrogen or progesterone receptor positive breast cancers has been associated with significant benefits such as decreased local and distant recurrences, a lower risk of contralateral breast cancer and improved breast cancer specific mortality (Coates et al 2007; Forbes et al 2008)
In order to address this clinical need for correct E2 measurements, the objective of the present study was to evaluate the accuracy of several different commercially available and commonly used E2 immunoassay kits regarding measurement of E2 levels in the serum of postmenopausal breast cancer patients treated with aromatase inhibitor (AI)
The findings of this study clearly emphasize the need for improved E2 immunoassay methods, or a complete change in methodology to ensure accurate and reliable serum E2 measurements for patients undergoing AI treatment
Summary
Hormone suppression in postmenopausal women with estrogen or progesterone receptor positive breast cancers has been associated with significant benefits such as decreased local and distant recurrences, a lower risk of contralateral breast cancer and improved breast cancer specific mortality (Coates et al 2007; Forbes et al 2008). In patients with early breast cancer, adjuvant therapy with aromatase inhibitors (AIs) was proven to lower 5-year relapse rates with improved side effect profiles. Third generation AIs suppress aromatase activity by 90 – 99%, which leads to a reduction of circulating estrogen levels to 1% to 10% compared with pretreatment levels (Santen et al 2007). By decreasing systemic estrogen significantly, AIs prevent growth of estrogen receptor positive micrometastases and dormant cancer cells (Howell et al 2005). Full benefits and optimal treatment outcome of postmenopausal breast cancer patients depend on maximally suppressed E2 levels
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