Advanced breast cancer in women with natural or artificially induced postmenopausal status, who have previously been treated with antiestrogens.

Letrozole binds to the heme group of aromatase, a cytochrome P450 enzyme which catalyzes conversion of androgens to estrogens (specifically, androstenedione to estrone and testosterone to estradiol). This leads to inhibition of the enzyme and a significant reduction in plasma estrogen levels; approximately 30% of human breast cancers are sensitive to this estrogen deprivation.

Letrozole is well absorbed, weakly protein binding, metabolized by CYP3A4 to a glucuronide metabolite, which is excreted in urine(90%), elimination half-life：2 days.

Hypersensitivity to letrozole or any component of the formulation, pre-menopausal women, pregnancy, lactation.

X

Avoided

Bone pain (22%), back pain (18%), nausea (15%), dyspnea (13%), arthralgia (12%), hot flashes (12%), headache (10%), fatigue (9%), cough (9%), constipation (8%), vomiting (7%), diarrhea (7%), hypertension (6%), abdominal pain (5%), peripheral edema (5%).

2.5 mg orally once daily; in severe hepatic impairment : 2.5mg Q2D.