Taking a daily dose of aspirin could significantly reduce breast cancer risk, according to the findings of a new study published in the journal Laboratory Investigation.
The study, led by Dr. Sushanta Banerjee, research director of the Cancer Research Unit at the Veterans Affairs Medical Center in Kansas City, MO, found that low-dose aspirin impaired the ability of breast cancer cells to renew. The researchers say their findings suggest that a daily dose of aspirin — a medication commonly used to relieve pain and prevent blood clots — could help to prevent the development and recurrence of breast cancer, the second most common type of cancer diagnosed among U.S. women.
Aspirin is already widely used. Tens of millions of people in the United States take it daily to reduce their risk of heart attack or stroke. But over the last two decades, a growing number of studies have suggested that taking aspirin on a regular basis may substantially lower a person’s risk of developing or dying from cancer, particularly cancers of the colon, stomach and esophagus, and possibly other types including breast, lung and prostate cancers. Regular aspirin use has also been linked to a reduced risk of metastatic cancer.
However, the research findings on aspirin use are not clear cut. Not every study of aspirin and cancer has shown that it reduces the risk of developing or dying from cancer. And most of the studies linking aspirin or other nonsteroidal anti-inflammatory drugs (NSAIDs) and a lower risk of developing or dying from cancer have had limitations; most have been either observational studies, which cannot establish causal effect, or analyses of clinical trials testing aspirin’s effect on other health measures, typically vascular outcomes.
There are also safety concerns associated with long-term aspirin use, such as the risk of internal bleeding, and experts say the evidence still isn’t clear enough to conclude whether or not the potential preventive benefits of aspirin (with respect to cancer) outweigh the potential harm. One of the key unanswered questions is how aspirin works to prevent cancer. Determining the mechanism(s) of action through which the drug inhibits cancer cell growth could “reshape the debate of risk and benefit,” write Dr. Banerjee and colleagues.
For the study, the researchers set out to identify potential mechanisms of action by testing the effects of aspirin 0n both incubated breast cancer cells in laboratory dishes and breast cancer tumors in mouse models. The experiment was designed to investigate two aspects of prevention: relapse prevention, which was tested by exposing cancer cells to aspirin, and primary prevention, which was assessed by putting healthy mice on a daily dose of aspirin and then exposing them to cancerous cells.
Daily low-dose aspirin almost halved breast tumor growth
For the cell test, the researchers incubated breast cancer cells in 96 separate dishes, exposing each one to various doses of acetylsalicylic acid, the chemical name for aspirin. According to Dr. Banerjee, exposure to aspirin “dramatically increased the rate of cell death in the test,” killing the majority of breast cancer cells. For those cells that did not die off, most were left unable to grow.
In the next phase of the experiment, the researchers gave ten mice with aggressive breast cancer tumors a daily dose of aspirin for 15 days. The dose they received was the equivalent to 75 milligrams in humans, which is considered to be a low dose. At the end of the 15 days, the researchers compared the tumor sizes of the treated mice with those of ten mice with aggressive breast cancer that did not receive aspirin. On average, the tumors of the mice that received the aspirin were found to be 47 percent smaller than those of the untreated mice.
In the final phase of the experiment, the researchers tested the preventive effects of aspirin by giving a daily dose of the drug to a group of healthy mice for 10 days, before exposing them to breast cancer cells. Compared with a control group, the mice that received the aspirin had significantly lower levels of cancerous growth.
“We found aspirin caused these [breast] cancer cells to lose their self-renewal properties,” explains Dr. Banerjee. “Basically, they couldn’t grow or reproduce. So there are two parts here. We could give aspirin after chemotherapy to prevent relapse and keep the pressure on, which we saw was effective in both the laboratory and the mouse model, and we could use it preventatively.”
While the findings are encouraging, it should be noted that each individual can have different reactions to medication and should seek advice from a health care provider before embarking on any form of drug regimen. Dr. Banerjee says he personally believes so strongly that the benefits of regular aspirin use outweigh the risks that, for three years, he has been on a daily aspirin regimen of his own. “Of course there is a risk,” he says, “but you have to weigh that against the risks of cancer.”
Before aspirin can be recommended for widespread use as a cancer prevention measure, experts say several key clinical questions still need to be answered. These questions include: what dose provides the most protection against cancer and the lowest risk of serious side effects; who is most likely to benefit from aspirin use; at what age should people start taking aspirin; how long should people take aspirin; which cancers does aspirin offer the most protection against; and how long after stopping aspirin does its anticancer protective effect last.