Letrozole
A non-steroidal aromatase inhibitor for hormone receptor-positive breast cancer after menopause, including after 5 years of tamoxifen.
Drug card
- Class
- Aromatase inhibitor
- How it works
- Blocking aromatase so androgens are no longer turned into estrogen
- Used for
- Early hormone receptor-positive breast cancer, after surgery
- Extended treatment after 5 years of tamoxifen
- Advanced breast cancer after menopause
- Lowering breast cancer risk in high-risk women
- Known for
- Hot flashes and night sweats
- Joint pain and stiffness
- Bone thinning (lower bone mineral density)
- Its name
- -rozole means a nonsteroidal aromatase inhibitor
Study it as a flashcard, and it comes back before you forget it.
Mechanism of action
How does letrozole work?
Letrozole is a non-steroidal competitive inhibitor that binds the heme of aromatase's cytochrome P450 unit, blocking conversion of androgens to estrogens in all tissues and lowering estrone, estradiol and estrone sulfate. It leaves adrenal glucocorticoid and mineralocorticoid synthesis largely untouched.
Like other aromatase inhibitors: After menopause most estrogen is made by aromatase, a cytochrome P450 enzyme in many tissues that turns androgens (androstenedione, testosterone) into estrogens (estrone, estradiol). Aromatase inhibitors block this final step, cutting estrogen in the blood and the tumor and so starving hormone receptor-positive breast cancer. Anastrozole and letrozole bind reversibly; exemestane, a steroid, binds irreversibly.
Uses
What is letrozole used for?
- Early hormone receptor-positive breast cancer, after surgery
- Extended treatment after 5 years of tamoxifen
- Advanced breast cancer after menopause
- Lowering breast cancer risk in high-risk women
Side effects
Side effects of letrozole
- Hot flashes and night sweatsKnown for
- Joint pain and stiffnessKnown for
- Bone thinning (lower bone mineral density)Known for
- Osteoporosis
- Broken bones (fractures)Serious
- High cholesterol
- Tiredness, dizziness and sleepiness
- Muscle and bone pain
- Swelling (edema)
- High blood pressure
- Hair thinning
- Vaginal bleeding
Known for marks what an exam expects you to know it for.
Watch for
Cautions and what sets it apart
- Contraindicated in pregnancy; a pregnancy test is done first in women who could become pregnant.
- Bone density, cholesterol and blood pressure are monitored during treatment.
- Tiredness, dizziness and sleepiness can make driving or using machinery unsafe.
- Cirrhosis or severe liver impairment roughly doubles exposure.
Good to know: It is also licensed for extended adjuvant treatment, continuing hormone therapy after 5 years of tamoxifen.
Remember it
A way to remember it
No aromatase, no estrogen, thinner bones
Blocking aromatase removes the main source of estrogen after menopause, and bone loses estrogen's protection: bone density falls and fractures rise, while tamoxifen, which acts like estrogen on bone, does not do this.
Written for biofideX
Its name
-rozole means nonsteroidal aromatase inhibitor
Anastrozole and letrozole block aromatase, cutting the estrogen made after menopause, and treat breast cancer. Exemestane, a steroidal aromatase inactivator, lacks the stem.
- Every drug name stem
Its class
Aromatase inhibitors
Other aromatase inhibitors with a card:
Easily mixed up with selective estrogen receptor modulators and 5-alpha reductase inhibitors.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.
Targeted therapy and the immune system
Letrozole is one of 13 drugs practiced together here: their classes, how they work, what they treat and what they're known for.
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