Can aspirin reduce the risk of breast Ca?

Women who take aspirin regularly are about 26% less likely to develop breast cancer than those who don't, according to New York researchers.

The population-based case–control study of almost 3,000 women with and without breast cancer found the association to be strongest among women who take at least one tablet of aspirin per day, among those who take aspirin alone or with other nonsteroidal anti-inflammatory drugs (NSAIDS) (as opposed to other NSAIDS alone), and among current and recent users (within the last 5 years). And they specifically found that aspirin protected most against hormone receptor-positive cancers, reducing the risk by 26% (OR 0.74, 95% CI 0.60–0.93). The findings did not pertain to ibuprofen or acetaminophen.

How might COX-2 inhibitors like aspirin slow down estrogen biosynthesis? In the receptor-positive breast cancer cell at the top of the drawing (1),, various tumor promotors stimulate production of the enzyme cyclooxygenase 2 (COX-2) which in turn is responsible for prostaglandin synthesis (2). Increased PGE₂ production then prompts the formation of aromatase (3) (4), the crucial enzyme that catalyzes the conversion of androgens to estrogens (5). The new research suggests that COX-2 inhibitors block prostaglandin synthesis, slowing down the long chain of events that leads to estrogen production in cancer cells.

While the mechanism of prevention is unclear, experts surmise that inhibition of estrogen biosynthesis plays an important role, as the illustration to the right suggests. While experts generally agree that it is too soon for all women to begin taking aspirin daily solely to prevent breast cancer, clinicians may want to consider this for women at highest risk.

Terry MB, Gammon MD, Zhang FF, et al. Association of frequency and duration of aspirin use and hormone receptor status with breast cancer risk. JAMA. 2004;291:2433-2440.