Letrozole suppresses plasma estradiol and estrone sulphate more completely than anastrozole in postmenopausal women with breast cancer.
OBJECTIVE
To compare the effects of anastrozole and letrozole on plasma estradiol (E2) and estrone sulfate (E1S) levels.


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).


CONCLUSIONS
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.
Dixon
J Michael
JM
Edinburgh Breast Unit, Western General Hospital, Edinburgh EH4 2XU, United Kingdom. jmd@ed.ac.uk
Renshaw
Lorna
L
Young
Oliver
O
Murray
Juliette
J
Macaskill
E Jane
EJ
McHugh
Mary
M
Folkerd
Elizabeth
E
Cameron
David A
DA
A'Hern
Roger P
RP
Dowsett
Mitch
M
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000077384:Anastrozole; D000970:Antineoplastic Agents / Q000627:therapeutic use*; D001943:Breast Neoplasms / Q000097:blood / Q000188:drug therapy*; D017024:Chemotherapy, Adjuvant; D018592:Cross-Over Studies; D004958:Estradiol / Q000097:blood; D004970:Estrone / Q000031:analogs & derivatives / Q000097:blood; D005260:Female; D006801:Humans; D000077289:Letrozole; D008875:Middle Aged; D009570:Nitriles / Q000627:therapeutic use*; D017698:Postmenopause; D011863:Radioimmunoassay; D020845:Selective Estrogen Receptor Modulators / Q000627:therapeutic use; D013629:Tamoxifen / Q000627:therapeutic use; D016896:Treatment Outcome; D014230:Triazoles / Q000627:therapeutic use*
D000970:Antineoplastic Agents; D009570:Nitriles; D020845:Selective Estrogen Receptor Modulators; D014230:Triazoles; D013629:Tamoxifen; D004970:Estrone; D000077384:Anastrozole; D004958:Estradiol; D000077289:Letrozole; C017296:estrone sulfate