Currently available radioimmunoassay methods for estradiol in serum lack sufficient sensitivity and precision to monitor estradiol levels in patients placed on third generation aromatase inhibitors. We recently validated a gas chromatography/tandem mass spectrometry assay (GC/MS/MS) for estradiol and determined estrogen levels in normal post-menopausal women and in women with breast cancer before and during administration of aromatase inhibitors. Validation of the GC/MS/MS assay in human plasma and human serum included determination of assay sensitivity (<0.63 pg/ml), precision (all CVs less than 17.8%), recovery (98-103%), and linearity of recovery (R = 0.998). Levels of estradiol were lower when assayed by GC/MS/MS compared to RIA under all conditions (7.26 ± 4.82 pg/ml versus 11.9 + 12.0 pg/ml in normal post-menopausal women; 5.88 ± 3.43 pg/ml versus 13.8 ± 7.5 pg/ml in breast cancer patients prior to treatment; and < 0.63 pg/ml versus 5.8 ± 4.1 pg/ml during aromatase inhibitor therapy). Fifty-five women treated either with atamestane/toremiphene or letrozole/placebo were monitored for estradiol levels at 4, 8 and 12 weeks of therapy. The mean levels of estradiol during aromatase inhibitor therapy was 5.8 ± 4.1 pg/ml as measured by RIA and <0.63 pg/ml by GC/MS/MS. The degree of suppression with the aromatase inhibitors as detected by RIA was 58% versus >89% by GC/MS. These results suggest that most RIA methods detect cross-reacting estrogen metabolites and yield higher measured levels than GC/MS/MS. Several pharmacological and clinical considerations suggest that GC/MS/MS should become the preferred method for monitoring aromatase inhibitor therapy.
All Science Journal Classification (ASJC) codes
- Molecular Biology
- Clinical Biochemistry
- Organic Chemistry