Regularly taking low-dose aspirin as recommended by a doctor has proven to be an effective way to reduce the risk of having another stroke or heart attack. But it may also protect against colorectal cancer, according to an Italian study published online April 22 in Cancer.

The study analyzed colorectal cancer cells from 238 people who previously had surgery for early-stage colorectal cancer from 2015 to 2019, 12% of whom had been taking low-dose (100 milligram) aspirin daily to prevent cardiovascular disease for at least one year prior to surgery.

How Aspirin May Protect Against Colorectal Cancer

Researchers found that aspirin users had significantly less cancer spread to the lymph nodes and a greater concentration of immune cells in the tumor compared with those who didn’t take a daily low-dose aspirin. The study also involved a corresponding exam of colorectal cancer cells in the lab, which exposed the cells to aspirin. In this analysis, they found higher levels of an immune modulator protein known as CD80, which helps control immune function. The increase appears to improve immune cells’ ability to alert other defense cells to the presence of proteins associated with colorectal tumors.

“We also found that in patients with rectal cancer, aspirin users had higher levels of CD80 in healthy rectal tissues, suggesting that aspirin enhances the immunity of the cellular environment in the colon,” says Marco Scarpa, a surgeon at University Hospital of Padova in Italy, one of the study’s principal investigators.

“Our study’s results suggest that aspirin might act in favor of the prevention and treatment of colorectal cancer, but only in the early stage of the disease,” Scarpa says. He notes that other large clinical trials have conversely shown an association between aspirin use and colorectal cancer mortality in later stages of the disease. “In more advanced cancer, including colorectal cancer, the molecular interaction is more complex and that’s likely when aspirin won’t work at all,” Scarpa says.

Adding Aspirin to Reduce Cancer Risk

The results of the study aren’t ready to be translated into clinical practice, Scarpa says. But it does add to the growing body of evidence suggesting that any cancer protection aspirin might provide can depend on the stage of the disease and the cancer type, which is true of cancer therapies in general.

“Just because a therapy is successful or not for one type of cancer doesn’t automatically tell you whether it will be successful or not for another type of cancer,” says Wendy Y. Chen, a medical oncologist with Dana-Farber Cancer Institute and an associate professor at Harvard Medical School in Boston.

Another clinical trial, published online April 29 in JAMA, involved 3,020 patients with high-risk, nonmetastatic breast cancer who took 300 milligrams of aspirin daily; the study found daily aspirin use to be ineffective. “Our definitive trial showed that for the early-stage, nonmetastatic breast cancer population, there doesn’t appear to be any benefit with aspirin in terms of decreasing recurrence risk or improving overall survival,” says Chen, who was the study’s lead author. “But there potentially could be a role for aspirin therapy for other types of cancer, or even a subtype of breast cancer.”

Add-Aspirin, a large ongoing study in the United Kingdom that is investigating whether taking daily aspirin after treatment for cancer stops or delays cancer from coming back, could provide more information about the relationship between aspirin use and breast cancer recurrence. “When the investigators report their results, our hope is that we will be able to pool some of our data to see if there would potentially be any particular subgroups of patients who might benefit from aspirin use for breast cancer,” Chen says.

Meanwhile, if you’re taking low-dose aspirin to help reduce your cardiovascular disease risk, Scarpa says you are also probably enjoying some protection from colorectal cancer.

Sandra Gordon is a medical writer in Stamford, Connecticut.