title: Superiority of gas chromatography/tandem mass spectrometry assay (GC/MS/MS) for estradiol for monitoring of aromatase inhibitor therapy.
abstract: 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.
authors.affiliation: University of Virginia, Charlottesville, VA 22908, United States. rjs5Y@virginia.edu <rjs5Y@virginia.edu>
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Santen
authors.forename: Lawrence
authors.initials: L
authors.lastname: Demers
authors.forename: Susan
authors.initials: S
authors.lastname: Ohorodnik
authors.forename: J
authors.initials: J
authors.lastname: Settlage
authors.forename: Peter
authors.initials: P
authors.lastname: Langecker
authors.forename: D
authors.initials: D
authors.lastname: Blanchett
authors.forename: Paul E
authors.initials: PE
authors.lastname: Goss
authors.forename: Shuping
authors.initials: S
authors.lastname: Wang
mesh_terms: D000735:Androstenedione / Q000031:analogs & derivatives / Q000627:therapeutic use; D047072:Aromatase Inhibitors / Q000627:therapeutic use*; D001681:Biological Assay; D001943:Breast Neoplasms / Q000097:blood / Q000188:drug therapy*; D004958:Estradiol / Q000097:blood*; D005260:Female; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D000077289:Letrozole; D009570:Nitriles / Q000627:therapeutic use; D010919:Placebos; D017698:Postmenopause; D011863:Radioimmunoassay; D012680:Sensitivity and Specificity; D053719:Tandem Mass Spectrometry; D014230:Triazoles / Q000627:therapeutic use
chemical_list: D047072:Aromatase Inhibitors; D009570:Nitriles; D010919:Placebos; D014230:Triazoles; D000735:Androstenedione; D004958:Estradiol; C048751:atamestane; D000077289:Letrozole