Incidence and Mortality
Globally, prostate cancer is the second most common cancer in men, and the most common amongst men in the UK and US. In 2008 there were an estimated 900,000 men diagnosed with prostate cancer worldwide and approximately 258,000 prostate cancer-related deaths. Since PSA testing has a much greater effect on prostate cancer incidence than mortality, the incidence of prostate cancer has been increasing over the last twenty years, but with little change or no rise in the number of deaths. Mortality rates are generally high in predominantly black populations (Caribbean and sub-Saharan Africa) and in countries such as USA, Australia, New Zealand and Western Europe and very low in Asia.
Risk Factors
Age is the main risk factor for prostate cancer, predominantly affecting men over the age of 50, with the average age of diagnosis being between 70 and 74 years. Men with a family history of prostate cancer and men of black African and black Caribbean descent are more at risk suggesting that important genetic determinants of risk also exist. There is some evidence to show that men carrying inherited mutations of the BRCA1 or BRCA2 genes have increased prostate cancer risk. Various studies have suggested that diet, obesity, smoking and exercise may also have an impact on men developing prostate cancer, but further evidence is required.
Diagnosis
Tests such as a urine test to rule out infection, a prostate specific antigen (PSA) blood test, a digital rectal examination and biopsy are used to diagnose the disease. The PSA test detects levels of a protein produced by cells of the prostate gland, but there are limitations as there are other possible reasons for an elevated PSA level such as inflammation. The rule is that the higher a man’s PSA level, the more likely it is that cancer is present. However, the use of the PSA testing is controversial as it often results in false positives. Performing biopsy, which is used in combination with PSA testing to diagnose prostate cancer, can result in side effects including impotence and incontinence. For these reasons, there is no approved screening programme for prostate cancer, but PSA testing may be offered to men over the age of 50 who are at increased risk of prostate cancer.
Types of Prostate Cancer
There are many types of prostate cancer, but the vast majority are adenocarcinomas (95%), mainly occurring in the peripheral zone of the prostate gland. They are the second most common malignancy found in men over 65. Other types include small cell carcinoma, which usually forms at nerve cells of the prostate gland, and squamous cell carcinoma, which is a non-glandular cancer. Both tumour types are very aggressive and are not associated with an increase in PSA levels making them difficult to detect.
Prognosis
The prognosis of prostate cancer has improved over the years, with almost 9 out of 10 prostate cancers being found at an early stage, but the survival trends are difficult to interpret. The rising survival rates are somewhat due to an earlier detection of tumours. However, it has been estimated that lead-time bias, which is defined as the difference in time between screen detection and clinical detection in the absence of screening, is also contributing to the rising survival rates. Five-year relative survival worldwide is 90% or more for disease which is confined to the prostate, but this falls to 30% for patients with metastatic disease at presentation.
PSA testing has contributed to detecting prostate cancer at an early stage and thus improving survival rates, but it is not specific enough to differentiate between early-stage invasive cancers and latent, non-lethal tumours that might otherwise have remained asymptomatic during a man’s lifetime. Men with less aggressive cancers can be closely monitored using PSA tests and repeat prostate biopsies as part of “active surveillance”, which aims to avoid or delay unnecessary treatment. Elderly men or men who suffer from other major illnesses and who are likely to die of other causes than prostate cancer, may be offered a “watchful waiting” approach, where they are monitored to assess cancer progression. This approach is far from optimal as there are limitations, possible side effects such as impotence and incontinence, and no definite prognosis. Thus, there is a great need to find better ways to differentiate which cancers will spread quickly compared to slower-growing tumours.
