Which of the following is a nonsteroidal aromatase inhibitor?

Letrozole is classified as a nonsteroidal aromatase inhibitor, meaning it works by blocking the aromatase enzyme, which is responsible for converting androgens into estrogens. This mechanism is particularly useful in the treatment of hormone receptor-positive breast cancer in postmenopausal women, as lowering estrogen levels can help slow the growth of certain types of breast tumors that require estrogen to grow.

The action of letrozole effectively reduces circulating estrogen levels, which can be a significant factor in managing the progression of hormone-sensitive breast cancers. It is important to note that aromatase inhibitors like letrozole are often preferred in specific clinical settings due to their side effect profiles compared to other forms of hormonal therapies.

In contrast, other choices in the list either do not serve the same function or belong to different categories of drugs. For example, exemestane is a steroidal aromatase inhibitor, not nonsteroidal, while testosterone does not have an inhibitory effect on aromatase as it primarily acts as a male sex hormone. Anastrozole is another effective nonsteroidal aromatase inhibitor and is often used for the same indications as letrozole, making it also a correct option if considered separately. However