Cancer Screening
Cancer screening programs are intended to detect cancer or precancerous conditions in asymptomatic individuals. The goal of cancer screening is to reduce the cancer death rate and, by detecting cancer early before signs or symptoms of cancer appear, improve the likelihood of successful treatment. However, because screening involves subjecting apparently healthy individuals to potential risk, population-based screening programs are recommended only when: a) the screening test has been shown to reduce mortality; b) the screening test is able to detect the disease in a pre-clinical phase; c) the test is able to accurately predict when cancer does exist (high sensitivity) and when it does not exist (high specificity); d) the test is considered safe and does not subject an individual to an unacceptable level of risk; and e) if a cancer is identified through screening, effective treatment is available.
Other factors that may be considered for screening is the acceptability of the test, the cost of the intervention, and the extent to which there is sufficient capacity in the system to not only perform the screening test, but to also provide follow-up diagnostic confirmation and treatment for those with abnormal test results.
Population-based screening is most effective and cost-efficient when offered through an organized screening program that incorporates all elements of the screening process, including evidence-based screening and follow-up guidelines and recruitment and retention strategies to maximize participation, as well as comprehensive quality assurance and information systems that support optimal program operation, monitoring and evaluation. Screening provided outside the context of an organized screening program is often referred to as "opportunistic" or "ad hoc" screening, and in Canada would involve at least some of the components of an organized program. However, lack of full organization may result in sub-optimal program operation, performance and resource efficiency.
Currently, there are only three cancers that meet all the requirements for government sponsored screening programs: cervical cancer; breast cancer; and colorectal cancer.
While there is continued progress in organized population-based screening in Canada, there is often insufficient scientific evidence for the government to support screening for a specific cancer either at a provincial or national level. Many of the specific cancer tests are expensive, invasive and participation of the population is, for the most part sub-optimal. For example, PSA (prostate specific antigen) test helps identify early prostate cancer (the most common diagnosed cancer in Canadian men the third most common cancer-related death, but there is insufficient scientific evidence to indicate that early detection decreases mortality. While screening trials are ongoing in both Europe and the USA to evaluate whether PSA screening reduces prostate cancer deaths rates, results are not yet scientifically conclusive. As another example, while there are screening trials for lung and ovarian cancers, there are no nationally co-ordinated efforts or recommendations for either lung or ovarian cancer in healthy asymptomatic individuals.
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