Questions remain as to whether aspirin is effective in helping the body fight against prostate cancer, according to scientists.
Taking aspirin causes the test results of men with prostate cancer to significantly improve by dropping their prostate specific antigen (PSA) levels, suggesting it is helping the body fight the disease.
PSA is a blood marker used to monitor the progress of prostate cancer.
However, scientists are still not certain that aspirin really does protect against the disease, which kills about 10,000 men in the UK each year.
The possibility remains that it might be delivering misleading signals by lowering PSA without affecting the disease.
If this true, it could also mean that aspirin is allowing some cancers to go undetected.
Dr Jay Fowke, from Vanderbilt University in Nashville, Tennessee, who led the research, said: "It will be important to understand which mechanism is in play because many men take nonsteroidal anti-inflammatory drugs for their cardiovascular health, so we need to know whether that reduces their prostate cancer risk, or simply reduces PSA, which would then be even less reliable as a marker of prostate cancer risk.
"Basing treatment on an artificially suppressed PSA score would also be problematic."