Low-dose aspirin linked with lower risk of several cancers

A large new study has found that people who took aspirin regularly for at least 4 years were 21 percent less likely 20 years later than those taking a placebo to have died from a solid-tumor cancer.  The study has received wide media attention, but there are some important details described in some—but not all—the coverage.

Following up on intriguing hints that aspirin use is related to lower cancer rates, University of Oxford researchers went back to investigate cancer death rates among 25,570 participants in large randomized trials conducted decades ago to test aspirin’s affect on heart disease and stroke. During the trials, which lasted an average of four years, they found about 20 percent fewer cancer deaths in people taking aspirin compared to people taking a placebo.

Drilling down further, the researchers found that nearly half the subjects had been tracked for up to 20 years after the trials ended. After several years in “dusty archives,” the lead researcher Dr. Peter Rothwell told a news conference, they found the outcomes for 12,000 people who had taken either aspirin or placebos in trials decades earlier.

Those taking aspirin had a 64% lower rate of death from esophageal cancer; 58% fewer deaths from stomach cancer; 49% fewer deaths from colorectal cancer; and 32% fewer deaths from lung cancer in nonsmokers.  Significantly they only began to see lower cancer death rates after five years for certain cancers; and it took 10 years to see the lower rates of colorectal cancer deaths.

[Note: These same researchers reported in Lancet last month on death and diagnosis rates specifically of colorectal cancer, using five randomized aspirin trials in Britain, Sweden, and the Netherlands. A 20-year followup found those who had taken aspirin 5 years or longer had about 25% fewer colon cancers (especially proximal cancers which are harder to detect), and a lower rate of rectal cancers; as well as one-third fewer deaths.]

Both the earlier study and the most recently one found no added benefit in taking more than 75 mg, but people in the longest-lasting trials (e.g. more than 7 years) showed the greatest reduction in overall cancer deaths.

These studies are important: They studied long-term outcomes in large numbers of people who’d participated in gold-standard randomized trials. However…the researchers and other experts are quick to caution against people rushing out to buy bottles of baby aspirin. Here are some of the caveats:

• The study’s lead author, Dr. Peter Rothwell, noted that most people in the aspirin-taking group stopped taking aspirin after the studies were finished; and others in the placebo group started taking aspirin. He suggested they might have seen even greater benefits if all subjects had taken aspirin the full 20 years, although others caution that they’d also want to track rates of complications of 20 years of low-dose aspirin.
• All experts warn that aspirin can cause bleeding in the stomach and intestines; and may pose further bleeding risks in elderly people who are particularly prone to falls.
• There was no added benefit in taking more than 75 mg of aspirin a day: In the U.S., “baby aspirin” has 81 mg, and one adult aspirin contains 300 mg (4 times the dose shown beneficial).
• Two-thirds of the British research subjects were men; further research is needed to observe outcomes in women taking low-dose aspirin.Salicylate is aspirin’s active ingredient, but researchers don’t know how it might work against cancer cells. In a test tube, scientists have seen both repair and self-destruction of faulty DNA cells enhanced by aspirin studies. Animal studies show that salicylate can suppress tumor growth.
• The current research will likely stimulate scientists to drill down further, to understand how salicytate affects different types of human cancer cells.

What people need to know:

• The current study is not strong enough by itself to recommend that healthy people at average risk for colorectal cancer should start taking low-dose aspirin, caution many experts.
• Those who are already taking a baby aspirin to decrease their risk for heart disease might be gaining some benefits in avoiding certain types of cancer.
• Because aspirin is a drug with known side effects, people should check with their doctor before starting daily low-dose aspirin.

Sources: Lancet online, 6 December 2010, and Vol 376, Issue 9754 Nov. 20; New York Times, LA Times, and multiple online medical sources.