Thankfully, the first randomized clinical trial is now going on in Britain, made possible by funding from a nonprofit group, Cancer Research UK. But the British study is looking at four cancers, and won’t be done until 2025. If we in the United States had funding to do a similar trial, we could combine our data and get answers much faster. If the United States is to maintain its role as the global leader in biomedical research, it must fund its own trial of aspirin in breast cancer.

Aspirin was originally derived from willow bark, which has been used as a painkiller since the time of Hippocrates. We don’t know exactly why it appears to work in fighting cancer. Aspirin reduces inflammation, and that may play a role in inhibiting the growth of tumors — perhaps by slowing the development of new blood vessels that nourish them, or by fighting old cells that keep growing when they should be dying off. It may also inhibit estrogen production, and we know that estrogen fuels the growth of most (but not all) breast cancers.

If we could prove that aspirin was an effective treatment in a clinical trial, it would have major implications, especially for low-income patients. Modern hormonal treatments, used after surgery to try to prevent cancer from recurring, last a standard five years and can cost between $1,200 and $2,300 a year. But not everyone who needs them is actually taking them. Higher co-pays reduce the number of women who fill their prescriptions, according to a 2011 study.

And that is just in the United States. Africa, Asia and Central and South America already account for more than 60 percent of the world’s cancer cases and about 70 percent of cancer deaths, according to the World Health Organization. The majority of the impact of the disease will be felt in those areas in the coming decades. Aspirin’s minimal cost would make it available in every country on earth, and for millions of women it could mean the difference between some treatment and none.

It may also offer an alternative treatment to women who cannot tolerate widely used cancer drugs because of debilitating side effects. For example, Columbia University researchers found that half of breast cancer patients taking hormonal treatments (specifically, tamoxifen and aromatase inhibitors) were unable to take the drugs for the recommended five years. A survey by the advocacy group Breast Cancer Action found that the predominant reason was joint pain. The most serious possible side effects of taking aspirin are gastrointestinal bleeding and stroke, but they are rare.