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J Clin Oncol. 2008 Apr 1;26(10):1671-6. doi: 10.1200/JCO.2007.13.9279.

Letrozole suppresses plasma estradiol and estrone sulphate more completely than anastrozole in postmenopausal women with breast cancer.

Author information

1
Edinburgh Breast Unit, Western General Hospital, Edinburgh EH4 2XU, United Kingdom. jmd@ed.ac.uk

Abstract

PURPOSE:

To compare the effects of anastrozole and letrozole on plasma estradiol (E2) and estrone sulfate (E1S) levels.

PATIENTS AND METHODS:

Fifty-four postmenopausal women with estrogen receptor-positive breast cancer receiving aromatase inhibitors (AIs) as part of their adjuvant therapy were randomly assigned to receive either 3 months of anastrozole (1 mg) followed by 3 months of letrozole (2.5 mg), both given orally once daily, or 3 months of the opposite sequence. Blood was taken at the same time and the same day of the week from each patient, before and after 3 months of each drug, and plasma levels of E2 and E1S were determined using highly sensitive radioimmunoassays.

RESULTS:

There were 27 patients in each group. The mean age of the patients was 63 years (range, 49 to 83 years). Baseline E2 levels ranged from 3 pmol/L to 91 pmol/L with a mean of 25.7 pmol/L. Only one of 54 (2%) patients had an E2 value >or= 3 pmol/L after receiving letrozole, versus 20 of 54 (37%) patients after receiving anastrozole (P < .001). Extrapolation revealed a mean E2 level after anastrozole treatment of 2.71 pmol/L (range, 2.38 to 3.08 pmol/L). Following letrozole, it was 1.56 pmol/L (range, 1.37 to 1.78 pmol/L). Mean residual E2 was 10.1% for anastrozole and 5.9% for letrozole. Residual E1S levels were 4.6% for anastrozole and 2.0% for letrozole (P = .001).

CONCLUSION:

Letrozole reduces plasma E2 and E1S levels to a significantly greater extent than anastrozole in postmenopausal women taking AIs as part of their adjuvant therapy for hormone receptor-positive breast cancer.

PMID:
18375896
DOI:
10.1200/JCO.2007.13.9279
[Indexed for MEDLINE]

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