Drug companies are pouring billions of dollars into developing new targeted therapies for cancer, and so far none are close to a cure. But there is a countervailing force to their quest: the search for widely available drugs that could stop cancer from starting. Chemoprevention, as the field is called, just got a win with the news that aspirin, already used to prevent heart disease, reduces the risk of the most common form of breast cancer.
No one is ready to recommend that women start popping aspirin every day, in part because the drug can cause gastro-intestinal side effects. But the report, in the May 26 issue of The Journal of the American Medical Association, does raise the hope that women already taking aspirin to prevent heart disease may be getting another valuable benefit. "I think this is a very important paper," says Dr. Waun Ki Hong, a pioneer in chemoprevention at the M.D. Anderson Cancer Center in Houston.
Hong says a number of drugs have now been shown to suppress cancer, including aspirin and similar non-steroidal anti-inflammatory drugs (NSAIDS) such as ibuprofin. In fact, aspirin has already proven effective in preventing colon cancer. A stream of studies over the last few years has also focused on aspirin's potential against breast cancer, but with mixed results. The JAMA study, by researchers from Columbia University, is noteworthy because it shows which type of breast cancer would most likely be prevented -- and why.
DOWNSIDE TO DAILY DOSES
The researchers studied 3,000 Long Island women, half with breast cancer and half without, and analyzed how often they took aspirin, ibuprofen (such as Advil), and acetaminophen (such as Tylenol). They found that 20.9% of the women with breast cancer had taken aspirin regularly for six months or longer before they were diagnosed, compared with 24.3% of the women in the control group. That adds up to a 20% lower risk of breast cancer for aspirin users vs. nonusers. The drug was most effective against tumors that are dependent on the hormones estrogen and progesterone, reducing the risk of these types of cancers by 26%. Hormone-dependent tumors account for 60% to 70% of all breast cancer cases. Ibuprofen had a weaker effect, while acetaminophen, which is not an NSAID, offered no protection.
The Columbia scientists based their study on 10 years of lab research. They knew that aspirin blocks an enzyme in the blood called COX-2 that stimulates estrogen production. Testing its effect in mice, Dr. Andrew J. Dannenberg of Weill-Cornell Medical College, a co-author of the JAMA report, found that aspirin reduced both estrogen and breast tumors.
Still, cancer experts say the Columbia study wasn't flawless. It only followed the women for a year, and was retrospective -- the outcomes were based on participants' reports of their own behavior and open to bias, a problem with many such studies. But more money is being poured into prospective trials, which give a drug to a large population over a number of years to see what happens. The National Cancer Institute is conducting a seven-year trial with 22,000 women to see whether tamoxifen, a breast cancer treatment, or Eli Lilly & Co.'s (LLY) Evista, an osteoporosis drug, is better able to prevent breast cancer. Results are due in 2006.
The NCI says there are more than 40 other drugs in chemoprevention trials, ranging from old standbys like aspirin to new targeted therapies such as AstraZeneca PLC's (AZN) Iressa, a lung cancer treatment approved in 2003. M.D. Anderson doctors are testing Iressa and Tarceva, a similar drug by Genentech (DNA) and OSI Pharmaceuticals (OSIP), in heavy smokers in an attempt to prevent lung cancer.
There can be a downside to giving a pill every day to prevent disease. Merck & Co.'s (MRK) anti-baldness drug, Proscar, was able in a large trial reported last year to reduce prostate cancer by 25%, but the men on Proscar who did develop cancer tended to get more deadly tumors, possibly because of the drug.
Still, cancer specialists are encouraged. "Oncology is two decades behind cardiology when it comes to disease prevention, but we are beginning to get smarter about it," says Dannenberg. The 212,000 women likely to be diagnosed with breast cancer in the U.S. this year can only hope so.
Corrections and Clarifications
"A preemptive strike against cancer" (News: Analysis & Commentary, June 7) and the accompanying table referred to Merck & Co.'s Proscar (finasteride) as an anti-baldness drug. Proscar, approved for the treatment of enlarged prostates, was able in a large trial to reduce risk of prostate cancer by 25%. Procepia (also finasteride) is used to treat baldness.
By Catherine Arnst in New York