A pooled analysis of 2 cohort studies suggested that individuals who began using aspirin before age 70 years and continued using the agent later in life had a reduced risk of colorectal cancer.
A pooled analysis of 2 cohort studies published in JAMA Oncology revealed that instituting aspirin into the treatment regimen of elderly adults was not associated with a lower risk of colorectal cancer (CRC). Instead, the study indicated that individuals who began using aspirin before age 70 years and continued using the agent later in life had a reduced risk of CRC.
Notably, previously reported findings from the randomized Aspirin in Reducing Events in the Elderly (ASPREE) study evaluated 19,114 relatively healthy adults aged 70 years or older (or 65 years or older for racial/ethnic minorities) and reported that patients assigned to daily low-dose aspirin had an increased risk of death from cancer, including CRC, without a corresponding increase in overall and CRC incidence. However, the majority of these study participants had never used aspirin regularly before study enrollment.
“Taken together with the results of the ASPREE trial, these findings suggest that initiation of aspirin use at an older age for the sole purpose of primary prevention of CRC should be discouraged,” wrote the study authors, who were led by Chuan-Guo Guo, MMed. “However, our findings appear to support recommendations to continue aspirin use if initiated at a younger age.”
Using the Nurses’ Health Study (NHS) and the Health Professionals Follow-up Study (HPFS), a total of 94,540 participants aged 70 years or older were included in the current analysis and followed through June 30, 2014, for women or January 31, 2014, for men. Of note, individuals with a diagnosis of any cancer, with the exception of nonmelanoma skin cancer or inflammatory bowel disease, were excluded from the study.
Of the total study cohort, there were 1431 incident cases of CRC documented over 996,463 person-years of follow-up.
Following adjustments for other risk factors, regular aspirin use was found to be associated with a significantly lower risk of CRC at or after age 70 years compared with risk in those who did not regularly use aspirin (HR, 0.80; 95% CI, 0.72-0.90). However, this inverse association was only evident among those who began their aspirin use before the age of 70 (HR, 0.80; 95% CI, 0.67-0.95). Contrastingly, starting aspirin use at 70 years or later was not significantly associated with a lower risk of developing CRC (HR, 0.92; 95% CI, 0.76-1.11).
“We acknowledge that the differential association of aspirin among those who initiated its use after 70 years of age may be due to a more limited duration of use. However, among those who initiated aspirin use after 70 years, we found that the lack of association of aspirin use with CRC was consistent among those who used for more than 5 years and those who used for less than 5 years,” the authors noted. “In addition, in many prior studies, aspirin use for at least 5 years was sufficient for an association to emerge.”
Importantly though, these results are not as definitive as those observed in a randomized clinical trial. However, such a trial would require a large number of participants initiating aspirin at different ages with follow-up beyond 70 years of age, thus limiting feasibility. Additionally, the NHS and HPFS are based on self-reported questionnaires, which may skew the results; however, the participants were also health professionals, making it more likely that the self-reported intake is reflective of actual use.
Given the collective findings, the investigators indicated that “further studies to elucidate biologic mechanisms of aspirin according to age are warranted.”
Guo C, Ma W, Drew DA, et al. Aspirin use and risk of colorectal cancer among older adults. JAMA Oncol. Published online January 21, 2021. doi: 10.1001/jamaoncol.2020.7338