Letrozole is primarily used in the treatment of hormone receptor-positive breast cancer in postmenopausal women. It works by inhibiting the enzyme aromatase, which reduces the production of estrogen, thereby slowing the growth of certain types of breast tumors that rely on estrogen. It is often prescribed as an adjuvant therapy following surgery or other treatments to prevent cancer recurrence. Additionally, letrozole is used in fertility treatments to stimulate ovulation in women with polycystic ovary syndrome (PCOS) or other ovulatory disorders. It is sometimes preferred over other medications due to its effectiveness and relatively mild side effect profile. In some cases, it is also utilized off-label for managing endometriosis or as part of hormone therapy regimens.