What type of aromatase inhibitors are irreversible?

Aromatase inhibitors function by blocking the aromatase enzyme, which is crucial for converting androgens into estrogens. There are two main types of aromatase inhibitors: steroidal and nonsteroidal.

Steroidal aromatase inhibitors, such as exemestane, are irreversible. They act by permanently binding to the aromatase enzyme, leading to a long-lasting inhibition of estrogen production. This characteristic makes steroidal inhibitors particularly effective in reducing estrogen levels over time, which is significant for treating hormone receptor-positive breast cancer.

In contrast, nonsteroidal aromatase inhibitors like anastrozole and letrozole are reversible. They bind to the aromatase enzyme in a way that can be undone, allowing for the potential restoration of enzyme activity. Hence, they do not provide the same long-term suppression of estrogen levels as steroidal inhibitors.

Understanding this distinction is important for effective cancer treatment strategies, as the choice between steroidal and nonsteroidal aromatase inhibitors can impact patient outcomes.