Oncolet 2.5 mg Oncolet 2.5 mg contains Letrozole 2.5 mg, a hormonal therapy used to treat hormone receptor-positive breast cancer in postmenopausal women. It works by lowering the amount of estrogen produced in the body, which helps slow or stop the growth of breast cancer cells that depend on this hormone. Oncolet may be used as an initial treatment, after surgery, or as extended therapy to help reduce the risk of cancer recurrence. It should be taken only as prescribed by an oncologist or healthcare professional.