Regular use of aspirin was associated with a 46% reduced relative risk for pancreatic cancer, according to a new case-control study from Chinese and US researchers.
"Regular use of aspirin thus appears to reduce risk of pancreatic cancer by almost half," conclude the authors, led by author Harvey Risch, MD, PhD, from the Department of Chronic Disease Epidemiology, Yale School of Public Health, New Haven, Connecticut.
Regular use was defined as at least one tablet (regular- or low-dose) per week for 3 months or longer at any point in the participant's life.
The study was published online December 20, 2016, in Cancer Epidemiology, Biomarkers & Prevention.
But another expert was cautious about the results.
"Compared to cohort studies, case-control studies are more prone to various biases, which tend to favor finding an association," said Andrew T. Chan, MD, MPH, a gastroenterologist at the Massachusetts General Hospital, Boston, who was asked for comment and has authored work about cancer risk and aspirin use.
"Nonetheless, the findings do suggest the possibility that aspirin may prevent pancreatic cancer. Further work is clearly needed," said Dr Chan in an email to Medscape Medical News.
In the new study, the investigators identified patients with newly diagnosed pancreatic cancer at 37 Shanghai hospitals from December 2006 to January 2011. The 761 cases were interviewed at home about aspirin use and their ages when the use started and stopped. They were matched with 794 control patients randomly identified from the Shanghai Residents Registry, who were also interviewed and had blood drawn.
Most of the participants had never used aspirin. Overall, there were 87 ever-users among the cases and 143 among controls. The median duration of use was 3.5 years among cases and 4 years among controls. But when the Chinese participants used aspirin, they used it very regularly. All but 6 of the 230 ever-users used aspirin at least daily.
The author report that ever-regular use of aspirin was associated with a significantly lowered risk for pancreatic cancer (odds ratio [OR], 0.54; 95% confidence interval [CI], 0.40 - 0.73; P = 10–4.2). Also, risk decreased 8% per each cumulative year of use (OR for trend, 0.92; 95% CI, 0.87 - 0.97; P = .0034).
Use of nonaspirin nonsteroidal anti-inflammatory drugs was not analyzed because only 12 people reported its use.
This is the second study from the Yale researchers that has found an approximately 50% reduced risk for pancreatic cancer associated with regular use of aspirin. The first was a case-control study among residents of Connecticut (Cancer Epidemiol Biomarkers Prev. 2014;23:1254-1263).
However, the literature on aspirin use and pancreatic cancer risk has mixed results. Among 18 observational studies that the team identified, 6 have shown significantly reduced risk with use and 12 have not, the authors say.
For example, in a prospective cohort study involving 135,000+ individuals published earlier this year by Dr Chan and colleagues, regular, long-term use of low-dose aspirin was linked to a small decrease in overall cancer risk, but most of the reduction was due to decreased gastrointestinal cancers, particularly colorectal cancer (JAMA Oncol. 2016;2:762-769).
"In our study, we did not observe a significantly decreased risk of pancreatic cancer associated with aspirin use," said Dr Chan, whose study was among the 18 looked at by Dr Risch's group.
Risks associated with aspirin use include gastric and brain bleeding, said Dr Risch in an email to Medscape Medical News. "Aspirin reduces platelet adhesiveness…and may cause some degree of stomach wall erosion with long-term use, so while these risks are low, they are not zero. Its use requires individual evaluation of familial and other risks and balancing the potential benefits with the potential harms," he said.
Currently, the American Cancer Society (ACS) does not recommend aspirin use for disease prophylaxis, an official told Medscape Medical News last year.
"The American Cancer Society recognizes the evidence that long-term, regular aspirin use has both harms and benefits, including reduced risk of colorectal cancer, but does not currently have recommendations for or against aspirin use," said Eric Jacobs, PhD, strategic director of pharmacoepidemiology at the ACS.
However, in 2015, the US Preventive Services Task Force recommended long-term (at least 10 years) daily low-dose aspirin for the prevention of cardiovascular disease (CVD) and colorectal cancer in adults aged 50 to 69 years who have increased CVD risk.
Dr Risch and colleagues suggest that the related aspirin use could have an additional benefit.
They write: "While the choice to use aspirin for disease prophylaxis generally depends upon evaluated risks of cardiovascular disease, colorectal cancer, etc., it is likely that such use at least does not increase risk of pancreatic cancer, and very probably appreciably lowers it."
The publishing of the new study prompted some criticism in the media because of press materials from Yale University that overstated the meaning of the results. The press release was headlined: "Aspirin Use Found to Lower Risk of Pancreatic Cancer."
The study and press materials were also criticized by healthnewsreview.org, a medical news and information watchdog group, for lacking context. Pancreatic cancer is relatively rare, and a result of a 50% reduction does not alter absolute risk much, the organization pointed out. "According to the American Cancer Society, a 60-year-old man has a 0.41% (1 in 241) chance of developing pancreatic cancer during the next 10 years. (Risk varies greatly with age and is much lower at younger ages.) So cutting that risk in half might bring it down to about 0.2% (1 in 480)," the article argued.
The study was supported by grants from the National Cancer Institute, Science and Technology Commission of Shanghai Municipality, and Shanghai Cancer Institute. The study authors have disclosed no relevant financial relationships. Dr Chan reports consulting for Bayer Healthcare, Pfizer Inc, and Pozen Inc.
Cancer Epidemiol Biomarkers Prev. Published online December 20, 2016. Abstrac