Oncofocus Test Kit
includes suggestions for Letrozole
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Femara (Letrozole) has been approved for the first-line treatment of postmenopausal women with hormone receptor positive or hormone receptor unknown locally advanced or metastatic breast cancer. The drug is a once-a-day oral treatment originally approved in 1997 for advanced breast cancer in postmenopausal women with disease progression following antiestrogen therapy.
Estrogen has been shown to stimulate the growth of certain hormone-dependent cancer cells. In postmenopausal women, estrogen is primarily produced from the conversion of adrenal androgens to estrogen. This conversion is catalyzed by an enzyme known as aromatase. Femara contains 2.5 mg of letrozole, a compound that blocks the action of aromatase and therefore inhibits the conversion of androgens to estrogens.
Advanced breast cancer is the second leading cause of cancer death among women in the United States. Over 120,000 American women have advanced breast cancer, and approximately half of the 182,000 newly diagnosed cases of breast cancer each year are in an advanced stage when detected.
Among other studies, Femara was evaluated in a randomized, double-blind, multinational phase III trial that compared Femara 2.5 mg to tamoxifen 20 mg in 907 postmenopausal women with locally advanced (stage IIIB) disease, metastatic breast cancer, or recurrences not amenable to treatment with surgery or radiotherapy. Results of the trial demonstrated that Femara delayed progression of advanced breast cancer for 9.4 months compared to 6.0 months for tamoxifen. Significant differences were also observed between Femara and tamoxifen in terms of objective response rate (30% vs. 20%), clinical benefit (49% vs. 38%) and time to treatment failure (9.1 months vs. 5.7 months). Femara and tamoxifen were equally well tolerated.
Reported adverse events for Femara vs. tamoxifen included (but are not limited to) the following:
- Bone pain (20% vs. 18%)
- Hot flushes (18% vs. 15%)
- Back pain (17% vs. 17%)
- Nausea (15% vs. 16%)
- Dyspnea (abnormal breathing) (14% vs. 15%)
- Arthralgia (severe joint pain) (14% vs. 13%)
- Fatigue (11% vs. 11%)
- Coughing (11% vs. 10%)
MECHANISM OF ACTION
Letrozole is a nonsteroidal competitive inhibitor of the aromatase enzyme system; it inhibits the conversion of androgens to estrogens. In adult non-tumor and tumor-bearing female animals, letrozole is as effective as ovariectomy in reducing uterine weight, elevating serum LH, and causing the regression of estrogen-dependent tumors. In contrast to ovariectomy, treatment with letrozole does not lead to an increase in serum FSH. Letrozole selectively inhibits gonadal steroidogenesis but has no significant effect on adrenal mineralocorticoid or glucocorticoid synthesis.
Letrozole inhibits the aromatase enzyme by competitively binding to the heme of the cytochrome P450 subunit of the enzyme, resulting in a reduction of estrogen biosynthesis in all tissues. Treatment of women with letrozole significantly lowers serum estrone, estradiol and estrone sulfate and has not been shown to significantly affect adrenal corticosteroid synthesis, aldosterone synthesis, or synthesis of thyroid hormones. (from Novartis Revised Package Insert).