The anti-cancer effects of aspirin are controversial in academic circles. New findings from the University of Oxford provide strong evidence for the anti-cancer effects of aspirin. Daily aspirin use reduces the incidence of adenocarcinoma in the long term, while its effect on mortality is also evident after several years, suggesting that aspirin inhibits tumor growth and metastasis. The results of the study were published online in the March issue of The Lancet. The study consisted of five large randomized controlled trials in cardiovascular patients in the UK, with the trial group taking aspirin (≥75 mg) daily and recording the incidence of cancer in all patients. The anti-metastatic effect of aspirin was then observed, with cancer patients classified according to tissue and clinical characteristics, adenocarcinoma vs. other. A total of 17,825 patients participated in the trial, and 987 patients were diagnosed with solid tumors during a mean follow-up period of 6.5 years (SD 2.0). Compared to controls, the aspirin trial group reduced the rate of distal cancer metastasis (all cancers, hazard ratio [HR] 0.64, 95% Cl 0.48-0.84, p=0.001; adenocarcinoma, HR 0.54, 95% Cl 0.38-0.77, p=0.0007, other solid tumors, HR 0.82, 95% Cl 0.53-1.28, p= 0.39), which was mainly aspirin reduced the odds of metastatic adenocarcinoma at initial diagnosis ((HR 0.69, 95% CI 0.50-0.95, p=0.02) and during follow-up (HR 0.45, 95% CI 0.28-0.72, p=0.0009), especially colorectal cancer (HR 0.26, 95% CI 0.11-0.57, p=0.0008). In absolute numbers, this means that adjuvant aspirin treatment prevented 1 in 5 cancer patients from metastasizing. Also, aspirin reduced mortality in advanced adenocarcinoma (HR 0.65, 95% CI 0.53-0.82, p=0.0002), but not in other cancers (HR 1.06, 95% CI 0.84-1.32, p=0.64). Subjects were gender-neutral, and the greatest benefit was observed in smokers. Low-dose, slow-release aspirin preparations resisted platelet agglutination but compromised bioavailability. Apparently, aspirin reduces mortality in cancer patients mainly because of its inhibitory effect on metastasis. The present study suggests that aspirin is useful in the treatment of certain cancers, particularly adenocarcinoma.