What is letrozole’s mechanism of action (MOA)?
Letrozole is an aromatase inhibitor. It blocks the enzyme aromatase, which is responsible for converting androgens into estrogens. By inhibiting aromatase, letrozole lowers estrogen levels in the body. This reduces estrogen-driven stimulation of hormone-sensitive tumors, which is why it’s used in certain cancers such as hormone receptor–positive breast cancer.
How does aromatase inhibition affect estrogen levels?
Aromatase is needed for peripheral (tissue) estrogen production. When letrozole inhibits aromatase, less estrogen is formed, leading to decreased circulating estrogen concentrations. With lower estrogen availability, tumor cells that rely on estrogen signaling have less growth support.
How does letrozole differ from other hormone therapies?
Letrozole works by stopping estrogen synthesis (aromatase inhibition). Other common hormone therapies may work differently—such as by blocking estrogen receptors—rather than reducing estrogen production.
What patient factors matter for how well the MOA works?
Because letrozole’s effect depends on lowering estrogen, it is most relevant when estrogen production and estrogen signaling drive tumor behavior (for example, estrogen receptor–positive disease). In patients with more “estrogen-independent” tumor biology, the benefit from lowering estrogen may be smaller.
Common clinical context where this MOA is used
Letrozole’s aromatase-inhibiting MOA is the basis for its use in hormone receptor–positive breast cancer, including settings where lowering estrogen is a key treatment goal.
Sources
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