The CAP trial (Cluster randomised triAl of PSA testing for Prostate cancer) is the largest trial of prostate cancer screening ever, addressing the controversial question as to whether a routine single PSA (prostate specific antigen) test can reduce deaths from prostate cancer.

Almost 409,000 men without known prostate cancer were either invited for a single PSA blood test or nothing, referred to as NHS standard care. Forty percent of the men invited to the blood test had this done, of whom around  4,700 had or later developed a cancer, compared to approximately 3,400 in the control group who developed prostate cancer over the 10-year follow-up period. During this period, there was no difference in the rate of men who died from prostate cancer, but longer studies are ongoing to see whether differences emerge as the treatment of prostate cancer has also become more effective over this timeframe.

Embedded within the CAP trial was the ProtecT (Prostate Testing for Cancer and Treatment) trial, looking at the best treatment for those prostate cancers detected within the CAP trial, enrolling over 3,000 men with early prostate cancer into the three treatment arms: surgery, radiotherapy, and surveillance (with further treatment if required), showing that surveillance is as effective as surgery or radiotherapy in preventing prostate cancer deaths, potentially saving thousands of men from life-changing treatment consequences.

Prostate cancer places a significant burden on public health globally, causing an estimated 6 million years of life lost in 2016, a figure that is forecast to rise to 12 million by 2040. Amongst UK males, prostate cancer is the most
commonly diagnosed cancer, affecting 1 in 8 men, and is the second commonest cause of cancer death. The CAP trial provided the first and only robust evidence comparing a low-intensity PSA-based screening strategy (a single screen) for prostate cancer with no additional screening, minimal contamination, and was designed to reduce overdetection and overtreatment while seeking a mortality benefit. It showed that while PSA-based screening increases
the detection of low-risk prostate cancers, it does not save lives.