Challenges of measuring accurate estradiol levels in aromatase inhibitor‐treated postmenopausal breast cancer patients on vaginal estrogen therapy

Abstract

Breast cancer patients who are taking adjuvant Aromatase Inhibitor (AI) therapy typically have extremely low estradiol levels, which are undetectable by routine clinical laboratories. Thus, it becomes difficult to assess the safety of interventions such as low‐dose vaginal estrogen, which may increase estradiol levels. In this study, we aimed to assess the utility of enzyme‐linked immunosorbent assay (ELISA) to measure low estradiol concentrations in breast cancer survivors on AI therapy treated with either vaginal estrogen or lubricant for atrophic vaginitis as a part of clinical trial. The samples were tested using two independent ELISA kits. Some of the samples were also evaluated using liquid chromatography‐tandem mass spectrometry (LC‐MS/MS) for comparison. We found that while the results by ELISA were reproducible, they were not accurate when compared to LC‐MS/MS. It is possible that medications or supplements may cross‐react with the ELISA reagents and confound the assessment; however, those were often not the reason for the discrepancy. Our results highlight the need for developing novel, reliable, and clinically accessible assays to measure ultra‐low estradiol levels to improve care of breast cancer survivors. At this stage, based on our findings, we recommend using MS‐based assays for estradiol quantitation for breast cancer survivors, whenever necessary.

Measuring serum oestrogen levels in breast cancer survivors using vaginal oestrogens: a systematic review

“…There was some variability of reported E2 levels between RIA and LC-MS on review of matched samples, but discordant E2 elevation was rare (2/63 participants with matched samples). Similar to REVIVE [ 33 ], Melisko et al found that LC-MS was more likely than RIA to detect an early rise in E2, 19% of participants had elevated E2 at 4 weeks with LC–MS vs. 1.5% with RIA. This study had a reasonable sample size, with most patients (63/76) having matched samples, allowing greater reliability of concordance assessment for testing methods.…”

“…Methods used to measure oestradiol and oestriol in selected studies included mass spectrometry and immunoassays; several studies used more than one with variable concordance [ 22 , 33 ]. Mass spectrometry detected oestradiol levels down to a lower limit between 1.0 pg/mL and 3.0 pg/mL [ 22 , 29 , 33 – 36 ].…”

“…Methods used to measure oestradiol and oestriol in selected studies included mass spectrometry and immunoassays; several studies used more than one with variable concordance [ 22 , 33 ]. Mass spectrometry detected oestradiol levels down to a lower limit between 1.0 pg/mL and 3.0 pg/mL [ 22 , 29 , 33 – 36 ]. Immunoassays such as ELISA (enzyme-linked immunosorbent assay), ECLIA (enhanced chemiluminiscence immunoassay) and RIA (radioimmunoassay) had lower detection limits ranging between 0.8 pg/mL and 10 pg/mL [ 22 , 28 , 30 , 32 – 34 , 36 ].…”

“…The REVIVE study [ 33 ], an ongoing open-label RCT, reported serum hormone levels for the first eight participants. This study compares a vaginal oestradiol ring (Estring®) which releases approximately 7.5mcg oestradiol daily for 90 days to a polycarbophil-based vaginal moisturiser (Replens ™) in women with HR+ EBC taking an AI.…”

Sex-dependent effects of multiple acute concurrent stresses on memory: a role for hippocampal estrogens

“…However, several issues were found here. Estradiol ELISAs have difficulties quantifying low concentrations, such as in males, ovariectomized, or aromatase-inhibited animals (Hsing et al, 2007 ; Huhtaniemi et al, 2012 ; Schumacher et al, 2015 ; Niravath et al, 2017 ). We have used the Calbiotech ELISA to distinguish proestrus and estrous female unextracted serum (Hokenson et al, 2021 ).…”