Taking a low dose of aspirin every day may significantly reduces the risk of many cancers and prevent tumors from spreading.

Study lead Prof. Rothwell from Oxford University said, "For most fit and healthy people, the most important things they can do to reduce their lifetime cancer risk is to give up smoking, take exercise and have a healthy diet. After that aspirin does seem to reduce the risk further - only by a small amount if there is no risk factor, but if there is a family history for something like colorectal cancer, it tips the balance in favour of aspirin."
Researchers found that taking a low (75-300mg) daily dose of aspirin cut the total number of cancer cases (particularly bowel cancer) by 25% within 3-years. Each year only 9 cancer cases per 1,000 were reported in the aspirin-taking group, compared with 12 per 1,000 for those taking dummy pills. It also reduced the risk of a cancer death by 15% within 5-years (sooner if the dose was higher than 300mg). The cancer death risk went down by 37% if a patient continued to take aspirin after 5-years.
Source-Medindia