Lead author Nancy Cook of Brigham and Women's Hospital and Harvard Medical School said the study was based on data from the Women's Health Study, which tracks more than 30,000 women age 45 and older, half of whom were randomized to take aspirin every other day, while the other half received a placebo, NBC News reported.
For the first decade of the study, the women were sent annual supplies of monthly calendar packs containing either aspirins or placebos. At six months, 12 months, and then annually, the women were sent questionnaires that asked about taking their medications on schedule, whether they'd experienced any adverse effects and if they had been diagnosed with cancer.
At the 10-year mark of the study there was no difference in the risk of cancer between those taking aspirin and those taking placebo, but at the end of the study there was still no difference between the groups when it came to breast and lung cancer.
However, there was a big difference when it came to colorectal cancer: 202 women in the aspirin group developed colorectal cancer as compared to 249 in the placebo group, the study said.