biology

Letrozole

Letrozole is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Letrozole rather than just read about it. In short: Letrozole, sold under the brand name Femara among others, is an aromatase inhibitor medication that is used in the treatment of breast cancer for post-menopausal women. It was patented in 1986 and approved for medical use in 1996.

Key takeaways

Letrozole belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Letrozole to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Letrozole from memory before moving on to harder problems.

Reference excerpt

Letrozole, sold under the brand name Femara among others, is an aromatase inhibitor medication that is used in the treatment of breast cancer for post-menopausal women. It was patented in 1986 and approved for medical use in 1996. In 2021, it was the 222nd most commonly prescribed medication in the United States, with more than 1 million prescriptions. It is on the World Health Organization's List of Essential Medicines.

Medical uses

Breast cancer

Letrozole is indicated for adjuvant treatment of postmenopausal women with hormone receptor positive early breast cancer; extended adjuvant treatment of postmenopausal women with early breast cancer who have received prior standard adjuvant tamoxifen therapy; first and second-line treatment of postmenopausal women with hormone receptor positive or unknown advanced breast cancer. Letrozole is approved by the United States Food and Drug Administration (FDA) for the treatment of local or metastatic breast cancer that is hormone receptor positive or has an unknown receptor status in postmenopausal women.

Comparison with tamoxifen Tamoxifen is also used to treat hormonally-responsive breast cancer, but it does so by interfering with the estrogen receptor. However, letrozole is effective only in post-menopausal women, in whom estrogen is produced predominantly in peripheral tissues (i.e. in adipose tissue, like that of the breast) and a number of sites in the brain. In pre-menopausal women, the main source of estrogen is from the ovaries not the peripheral tissues, and letrozole is ineffective. In the BIG 1–98 Study, of post-menopausal women with hormonally-responsive breast cancer, letrozole reduced the recurrence of cancer, but did not change survival rate, compared to tamoxifen.

Ovulation induction

Letrozole is recommended as the first-line medication for ovulation induction in polyendocrine metabolic ovarian syndrome. Compared to clomiphene (Clomid), it causes higher number of ovulation and live birth rates. It has the same rate of multiple pregnancies (such as twins), and the same rate of miscarriages. The use of letrozole is typically off-label, and some countries may not allow off-label use. India banned the usage of letrozole in 2011, citing potential risks to infants while in 2012, an Indian parliamentary committee said that their office of the drug controller had colluded with letrozole's makers to approve the drug for infertility in India. The committee also stated that letrozole's use for infertility was illegal worldwide.

Medical abortion Studies have shown that the efficacy of first-trimester misoprostol-only medical abortion can be improved by the addition of letrozole.

Use in sports Letrozole is considered a performance enhancing drug by the World Antidoping Agency (WADA), as are other aromatase inhibitors, because they may be used to counteract the side effects of anabolic steroids. Letrozole itself is not a performance enhancer.

Contraindications Letrozole is contraindicated in women having a pre-menopausal hormonal status. Precautions are advised against becoming pregnant while using letrozole; on the loss of bone mineral density; on the increased level of cholesterol and fat in the blood; and on dizziness and against driving. Breast feeding (lactation) is also counterindicated.

Side effects The most common side effects are sweating, hot flushes, arthralgia (joint pain), and fatigue. Generally, side effects include signs and symptoms of hypoestrogenism. There is concern that long term use may lead to osteoporosis, which is why in certain patient populations such as post-menopausal women or osteoporotics, bisphosphonates may also be prescribed.

Interactions Letrozole inhibits the liver enzyme CYP2A6, and to a lesser extent CYP2C19, in vitro, but no relevant interactions with drugs like cimetidine and warfarin have been observed. Letrozole also inhibits CYP2A7.

Pharmacology

Pharmacodynamics Letrozole is an orally active, nonsteroidal, selective aromatase inhibitor and hence an antiestrogen. It prevents aromatase from producing estrogens by competitive, reversible binding to the heme of its cytochrome P450 unit. The action is specific, and letrozole does not reduce production of corticosteroids.

Research The antiestrogen action of letrozole has been shown to be useful in pretreatment for termination of pregnancy, in combination with misoprostol. It can be used in place of mifepristone, which is expensive and unavailable in many countries. Letrozole is sometimes used as a treatment for gynecomastia, although it is probably most effective at this if caught in an early stage (such as in users of anabolic steroids). Some studies have shown that letrozole can be used to promote spermatogenesis in male patients with nonobstructive azoospermia. Letrozole has also been shown to delay the fusing of the growth plates in mice. When used in combination with growth hormone, letrozole has been shown effective in one adolescent boy with a short stature. Letrozole has also been used to treat endometriosis. Endometrial stromal sarcomas are hormonally sensitive tumors as it is represented that letrozole reduces serum estrogen levels. Letrozole is well-tolerated and is a good option for long-term management of this disease. Also in a study on Uterine myoma the volume was successfully reduced by use of an aromatase inhibitor. Rapid onset of action and avoidance of initial gonadotropin flare with an aromatase inhibitor. Letrozole has been documented to be safe and effective for improving height and pubertal outcomes in children living with constitutional delay in growth and puberty, and is better than testosterone with regard to improvement in testicular volume and delaying bone-age progression. This was documented in a meta-analysis published by Dutta et al. which analyzed data from 7 different randomized controlled trials.

References

Illustrations

Worked examples

Example 1 — a first encounter with Letrozole

Start with the simplest possible case. Write down what Letrozole claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Letrozole before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Letrozole ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Letrozole

In research: Letrozole appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Letrozole in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Letrozole is common in secondary-school and first-year university syllabi. It links to neighbouring topics Aromatase inhibitors, Benzonitriles, CYP2A6 inhibitors, so understanding it makes those chapters shorter.
In everyday life: Look for Letrozole outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “Letrozole” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Letrozole in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Letrozole means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Letrozole out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Letrozole in simple terms?

Why does Letrozole matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Letrozole?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Letrozole.