New research suggests that initiating aspirin use in older patients is not associated with a lower risk of colorectal cancer in these individuals.
Nevertheless, the pooled analysis of two cohort studies found that people who used aspirin before 70 years of age and continued into their 70s or later had a reduced risk of colorectal cancer.
Reporting in a recent issue of JAMA Oncology, a multi-center team of investigators explained that aspirin is recommended for the prevention of colorectal cancer among adults between 50 and 59 years of age. Nevertheless, the recent ASPREE trial found conflicting results, and suggested a lack of benefit – and perhaps even possible harm – among older adults who take aspirin for this purpose.
To help shed light on these conflicting findings, the researchers set to examine the association between aspirin use and the risk of incident colorectal cancer among older adults.
To do so, they conducted a pooled analysis of two large US cohort studies: the Nurses’ Health Study (June 1, 1980 - June 30, 2014) and the Health Professionals Follow-up Study (January 1, 1986 - January 31, 2014), which together comprised 94,540 participants at least 70 years of age. These individuals were followed through either January 31, 2014 (for men) or June 30, 2014 (for women). Participants who had a pre-existing diagnosis of any cancer – except nonmelanoma skin cancer or inflammatory bowel disease – were excluded from the analysis.
The final cohort comprised 67,223 women (mean age 76.4 years; 97.1% White) and 27,317 men (mean age 77.7 years 96.0% White). Among these, a total of 1,431 incident cases of colorectal cancer were documented (857 in women; 574 in men) over 996,463 person-years of follow-up.
According to principal investigator Chuan-Guo Guo, MMed, of Massachusetts General Hospital and Harvard Medical School, the study found that the regular use of aspirin was associated with a significantly lower risk of colorectal cancer at or after age 70 years when compared with non-regular aspirin use (hazard ratio 0.80). This finding was consistent for both women and men, and were largely comparable in analyses according to colorectal cancer stage.
On the other hand, the inverse association was only apparent among those aspirin users who initiated such use before the age of 70 (HR 0.80).
Interestingly, among patients who did not regularly use aspirin before 70 years of age, initiating regular aspirin use at or after that age was not found to be significantly associated with decreased risk of colorectal cancer (HR 0.92; 95% CI: 0.76-1.11). These findings, the researchers added, were consistent after adjustment for a series of possible confounding factors, including use of cholesterol-lowering drugs, hyperlipidemia, hypertension, and cardiovascular disease.
The authors also analyzed their results according to the duration of aspirin use and the age of aspirin treatment initiation. These analyses found that the apparent protective benefits of aspirin use at or after 70 years were only evident in those people who had regularly used aspirin for at least five years before the age of 70 (pooled HR 0.76; 95% CI, 0.59-0.98). On the other hand, no benefit was seen in those people who used aspirin for less than five years before reaching age 70 (pooled HR 1.00; 95% CI: 0.77-1.30). With respect to the age at which aspirin use was initiated, lower risk of colorectal cancer for aspirin use at or after 70 years was only found when patients initiated aspirin before 70 years of age
In light of these findings, the investigators concluded that regularly using aspirin once reaching 70 years of age may help lower the risk of colorectal cancer, but only if initiated prior to reaching 70.
“Taken together with the results of the ASPREE trial,” the authors concluded, “these findings suggest that initiation of aspirin use at an older age for the sole purpose of primary prevention of colorectal cancer should be discouraged. However, our findings appear to support recommendations to continue aspirin use if initiated at a younger age.”
