"Take two (or so) and call me in the morning (or next week or next month or next year)."

A large study that was just published shows that women with breast cancer who take aspirin are more likely to live longer and to not have a cancer recurrence than women who don't take aspirin.

Doctors at three Boston-area hospitals observed 4,164 female registered
nurses in the Nurses’ Health Study who were diagnosed with stages I, II, or III breast cancer between 1976 and 2002. They were observed until June 2006, or death, whichever came first.

The main outcome was breast cancer mortality risk according to number of days per week of aspirin use (0, 1, 2 to 5, or 6 to 7 days) first assessed at least 12 months after diagnosis and updated..There were 341 breast cancer deaths. Aspirin use was associated with a decreased risk of breast cancer death.

Full report here.

The study says of itself that it's unprecedented: Of several large prospective studies of the association of aspirin use with breast cancer incidence, only one found a protective association, whereas four others did not. The 10-year Women’s Health Study Trial found no effect of low-dose aspirin intake (100 mg every
other day) on breast cancer incidence among almost 40,000 women. However, meta-analyses of either NSAID [non-steroidal anti-inflammatory agents/analgesics such as aspirin, ibuprofen, and naproxen] or aspirin have found a 9% to 30% reduced risk of breast cancer incidence. Despite inconclusive evidence linking aspirin and breast cancer incidence, aspirin may improve survival through various mechanisms.

To our knowledge, this is the first study reporting a survival
advantage among women with breast cancer who take aspirin. Abundant
scientific evidence supports why aspirin may confer this advantage.
More than 2 million US women are living after a breast cancer
diagnosis6 Survival among women with breast cancer is variable, and
risks of dying of the disease are elevated even 10 or 15 years after
diagnosis.

How much aspirin is helpful? I kept reading reports about this and couldn't find the number of milligrams. I'm especially interested because I take 162 mg. for polycythemia vera. What a nice surprise it would be if something I take for one disease would help me survive another. Alas, the researchers admit: We
lack details on aspirin dose. If there is a dose response, the effect size in
the current study may be diminished because frequent aspirin users
may be more likely to be low-dose users attempting to prevent heart
disease. Confounding is always a limitation of observational studies.
We addressed this by adjusting for all relevant covariates and through
marginal structural models.

Another caveat: Our results may be generalizable only to longer term breast
cancer survivors (ie, only women who have lived long enough after
diagnosis to report aspirin use after diagnosis, which is approximately
4 years). Fortunately, almost 90% of women diagnosed with breast
cancer live at least 5 years. Thus, our findings have considerable
clinical importance.

"Take-home message," as they say in business: It couldn't hoit. Aspirin has relatively benign adverse effects compared with cancer chemotherapeutic drugs and may also prevent colon cancer, cardiovascular disease, and stroke.

One skeptic has already pointed out that this is an observational study that does not prove cause and effect.