Aspirin Tied to Lower Colon Cancer Risk—for Some

Aspirin users with high levels of colonic enzyme had half the risk of developing colon cancer

Image: Chaval Brasil via Wikimedia Commons

The humble aspirin may have another beneficial effect beyond easing the pain of headache and reducing the risk of heart attack: lowering colon cancer risk among people with high levels of a specific enzyme.

The finding comes from a multi-institutional team that analyzed data and samples from two long-term studies involving nearly 128,000 participants. The researchers discovered that people who took aspirin and had high levels of a specific enzyme in their colons had half the risk of developing colorectal cancer compared with people who also took aspirin but whose colons showed low levels of the enzyme, called 15-hydroxyprostaglandin dehydrogenase, or 15-PGDH for short. About half of the population possesses high levels of 15-PGDH.

The results appear in the April 23 edition of Science Translational Medicine. While previous trials and prospective studies have shown that aspirin use reduces colorectal cancer risk, this retrospective study may explain why aspirin benefits some people, but not others.

The research team included scientists from Brigham and Women’s Hospital, Case Western Reserve School of Medicine, Dana-Farber Cancer Institute, Harvard Medical School, Massachusetts General Hospital and University Hospitals Case Medical Center.

“If you looked at the folks from the study who had high 15-PGDH levels and took aspirin, they cut their risk of colon cancer by half,” said senior author Sanford Markowitz, Ingalls Professor of Cancer Genetics at Case Western Reserve School of Medicine. “If you looked at the folks from the study who were low for 15-PGDH, they did not benefit at all from taking aspirin. These findings represent a clean Yes-No about who would benefit from aspirin.”

According to the American Cancer Society, colorectal cancer is the second leading cause of cancer-related deaths in the United States, with predictions that 137,000 Americans will develop the disease and 50,000 will die from it in 2014.

In the current study, the scientists built on earlier research indicating that regular use of non-steroidal anti-inflammatory drugs (NSAIDs), including aspirin, reduces the risk of developing colon cancer for some but not all individuals. Markowitz, also a medical oncologist at University Hospitals Case Medical Center, joined co-senior author Andrew Chan, HMS associate professor of medicine and a gastroenterologist at Mass General, to explore whether the presence of 15-PGDH led to different outcomes in developing colon cancer.

They hope to develop a test to guide physicians and patients in determining whether aspirin would help them.

The team examined tissues of 270 colon cancer patients who were among 127,865 participants followed for more than 30 years in the Harvard-based Nurses’ Health Study and Health Professionals Follow-up Study. Previous reports from the Mass General and Dana-Farber team showed that participants in these studies who regularly took aspirin had a lower risk of colorectal cancer. In earlier research, Case Western Reserve investigators and Monica Bertagnolli, HMS professor of surgery at Brigham and Women’s, had found that 15-PGDH appeared to enhance the ability of celecoxib, an anti-inflammatory medication commonly known as Celebrex, to prevent colon tumors in mice and in 16 humans tested. But when 15-PGDH was low or absent, celecoxib did not prevent colon tumors in mice or humans.

In the latest study, the investigators combined forces in a larger study to examine whether 15-PGDH levels might also be associated with the colon cancer-preventing benefits of aspirin, which lacks the adverse cardiovascular side effects of celecoxib.

The Mass General and Dana-Farber team dissected normal colon tissue from the pathology specimens of participants who developed colon cancer over the studies’ follow-up periods. The team at Case Western Reserve then analyzed these colon tissues to identify which among them had high or low levels of colon 15-PGDH. The investigators at Mass General and Dana-Farber examined how participants’ aspirin use and levels of 15-PGDH might be related to the risk of colorectal cancer.

The study’s results could lead to a test that would allow more personalized decisions about treatment to prevent colorectal cancer. People whose 15-PGDH levels indicate aspirin would have little benefit might choose to avoid the potential gastrointestinal side effects—such as stomach ulcers—that can accompany aspirin use. The researchers plan to develop a cost-effective and accessible test for measuring 15-PGDH in the colon. Chan and Markowitz believe such a test could become part of current medical practice. 

“During a colonoscopy, a gastroenterologist could easily and safely take an additional biopsy from the colon in individuals for whom preventive aspirin treatment might be appropriate,” Chan said. 

“There would be no reason why a good hospital pathology laboratory could not establish the test for 15-PGDH,” Markowitz said.

To confirm their findings, the study authors hope to launch a randomized, prospective clinical trial in which high-risk patients would be identified, treated with aspirin or a placebo, and monitored for development of colorectal tumors.

The mechanisms of action in 15-PGDH and in aspirin make them key players in colon cancer, the scientists said. Prostaglandins promote development of colon cancer. Aspirin helps prevent colon cancer development by blocking prostaglandins from being generated, while 15-PGDH helps prevent colon cancer development by catalyzing a reaction that “chews up” prostaglandins. Markowitz refers to the gene that produces 15-PGDH as the body’s genetic form of aspirin. The study suggests that both aspirin and 15-PGDH must work together to effectively prevent colon cancer, bringing the most benefit to individuals who have high levels of 15-PGDH.

“This study highlights the benefits of the relatively new practice of molecular pathological epidemiology, ” said co-senior author Shuji Ogino, HMS associate professor of pathology at Brigham and Women’s and Dana-Farber. “The molecular pathology part relates to analysis of 15-PGDH gene expression level in the normal colon to classify cancer based on molecular pathogenesis, while the epidemiology part relates to collection and analysis of aspirin use data in a population. This is an integration of these analyses."

Other researchers involved in the study include first author Stephen Fink, an instructor at Case Western Reserve; co-authors Mai Yamauchi and Reiko Nishihara, HMS research fellows at Dana-Farber; and senior author Charles S. Fuchs, HMS professor of medicine at Dana-Farber.

The study was supported by the Entertainment Industry Foundation’s National Colorectal Cancer Research Alliance; the National Cancer Institute’s GI-SPORE program (Specialized Programs of Research Excellence in Gastrointestinal Cancers) and Early Detection Research Network; National Institutes of Health grants P01 CA87969, P01 CA55075, 1UM1 CA167552, R01 CA136950, P50 CA127003, R01 CA151993, P50 CA150964, U01 CA152756, R01 CA137178 and K24 DK 098311; the Damon Runyon Cancer Research Foundation; and gifts from the Cleveland-based Marguerite Wilson Foundation, the Leonard and Joan Horvitz Foundation, the Richard Horvitz and Erica Hartman-Horvitz Foundation, and the Boston-based Bennett Family Fund for Targeted Therapies Research.

Adapted from a joint Case Western Reserve and Mass General news release.