Letrozole is Superior to Anastrozole in Suppressing Breast Cancer Tissue and Plasma Estrogen Levels
Purpose: To evaluate the influence of the third-generation aromatase inhibitor letrozole (Femara) on breast cancer tissue levels of estrone (E 1 ), estradiol (E 2 ), and estrone sulfate (E 1 S) in postmenopausal women undergoing primary treatment for locally advanced estrogen receptor/progesterone r...
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Veröffentlicht in: | Clinical cancer research 2008-10, Vol.14 (19), p.6330-6335 |
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Zusammenfassung: | Purpose: To evaluate the influence of the third-generation aromatase inhibitor letrozole (Femara) on breast cancer tissue levels of
estrone (E 1 ), estradiol (E 2 ), and estrone sulfate (E 1 S) in postmenopausal women undergoing primary treatment for locally advanced estrogen receptor/progesterone receptor–positive
breast cancers.
Experimental Design: Breast cancer tissue samples were collected before and following 4 months of neoadjuvant therapy with letrozole (2.5 mg o.d.),
and tissue estrogen levels measured using a highly sensitive RIA after high-pressure liquid chromatography purification.
Results: Letrozole suppressed pretreatment tumor levels of E 2 , E 1 , and E 1 S by 97.6%, 90.7%, and 90.1%, respectively. These data reveal that letrozole suppresses tissue estrogen levels significantly
below what has previously been recorded with anastrozole (89.0%, 83.4%, and 72.9% suppression, respectively) using the same
methods. To confirm the differential effect of letrozole and anastrozole on each plasma estrogen fraction, we re-analyzed
plasma samples obtained from a previous intrapatient cross-over study comparing letrozole and anastrozole using an improved
RIA (detection limits of 0.67, 1.14, and 0.55 pmol/L for E 2 , E 1 , and E 1 S, respectively). Letrozole consistently suppressed each plasma estrogen fraction below the levels recorded for anastrozole:
E 2 (average suppression by 95.2% versus 92.8%; P = 0.018), E 1 (98.8% suppression versus 96.3%; P = 0.003), and E 1 S (98.9% suppression versus 95.3%; P = 0.003).
Conclusion: Our data reveals that letrozole (2.5 mg o.d.) is more effective compared with anastrozole (1.0 mg o.d.) with respect to tissue
as well as plasma estrogen suppression in patients with postmenopausal breast cancer. |
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ISSN: | 1078-0432 1557-3265 |
DOI: | 10.1158/1078-0432.CCR-07-5221 |