Most cancer screening across the world is opportunistic, but some countries have regionally or nationally organized programs, in which every stage of the screening process from the invitation to participate, to the follow-up of abnormal results is organized and monitored by a central body. Opportunistic screening is dependent on the individual requesting a screening test or the health-care provider offering it, whereas organized screening depends on databases with information on the target population from which invitations are produced automatically. Both systems have advantages and disadvantages, but in general, organized programs usually offer free or subsidized tests, are able to achieve greater coverage, and minimize social inequalities in access (although not necessarily in uptake), by making sure everyone in the population who is eligible is invited (Miles et al, 2004). However, they could be criticized for reducing the opportunity for patient-provider interaction to discuss the test and for lacking the flexibility to match screening recommendations to patient characteristics - organized programs will occasionally issue invitations for cervical screening to women who have no cervix, or FOB test kits to people who have just been treated for colorectal cancer; something that would be much less likely in an opportunistic screening context.
Information on the availability of screening services worldwide is collated by the International Cancer Screening Network (ICSN) which is sponsored by the National
Cancer Institute (http://appliedresearch.cancer. gov/icsn/). Starting in 1988 with just 11 countries, the ICSN now reports on screening services that are available across 28 countries in Europe, Asia, Australasia, and the Americas. Even in countries without an organized program, most publicize recommendations on which cancers to screen for, the age of the population to be screened, and the optimal frequency of testing. For example, the US Centers for Disease Control and Prevention advocates screening as recommended by the US Preventive Services Task Force (http://www. ahrq.gov/clinic/uspstfix.htm), and the European Council provides screening guidelines for all the countries in the European Union (http:// ec.europa.eu/health/ph_determinants/genetics/ cancer_screening_en.pdf).
Cervical screening is currently offered to women in most developed countries. This is usually by Pap testing, but there has recently been a move to using liquid-based cytology in some countries. The USA and Canada offer cervical screening opportunistically, but organized programs are offered in Australia, the UK, and some other European countries. In a survey of 25 European screening centers (from 18 countries), organized screening was offered by 15 and opportunistic screening by 10 centers (Anttila et al, 2004). The age that cervical screening starts ranges from 18 to 30 years, and screening usually finishes between 60 and 69 years. Recommended screening intervals vary widely across countries (from 1 to 10 years) and in some countries depend on the age of the woman and whether she has had a previous abnormal result. Across Europe, the number of Pap tests a woman has in her life time therefore ranges from 7 to 50 (Anttila et al, 2004).
Organized breast screening with mammog-raphy is offered in Canada, Australia, New Zealand, Japan, Korea, and most of Europe, with opportunistic screening in the USA and Brazil. The age ranges for screening vary, but the lower limit is between 40 and 50 years, and the upper limit between 69 and 74 years. Recommended screening intervals also vary, ranging from 1 to 3 years (Shapiro et al, 1998; Klabunde and Ballard-Barbash, 2007). In the USA, the Preventive Services Task Force recently changed its mammography guidelines and now recommends against breast screening for women below the age of 50 and suggests biennial rather than annual screening (USPSTF, 2009).
Colorectal cancer screening most commonly uses FOB testing, but can include sigmoi-doscopy or colonoscopy. Screening is offered to men and women from 45 to 60 years up until 64-80 years of age, with no upper age limit in some countries. The interval depends on the type of test: for FOB testing most screening is every 1-2 years, but flexible sigmoidoscopy or colonoscopy is only required once or every 5-10 years (Benson et al, 2008). Screening for colorectal cancer is available in the USA, Australia, the UK, and several countries in Europe and Asia. Only 12 countries currently offer national organized screening programs (Australia, Cyprus, Czech Republic, England, Finland, France, Israel, Japan, Korea, Poland, Portugal, Scotland, and Slovenia) but other countries have organized regional programs (Power et al, 2009).
Controversy surrounding the specificity of the PSA test means there are currently no organized prostate cancer screening programs. In combination with the Digital Rectal Exam, PSA testing is offered opportunistically to men over the age of 50 years in several countries including the USA, Canada, the UK, and Australia. In the USA, men are offered the test annually as part of a regular health check. The UK allows any man over the age of 50 who asks for a PSA test to have one, but only after discussion of the implications with the provider.
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