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Cancer screening involves efforts to detect cancer before symptoms appear.[1] This may involve blood tests, urine tests, other tests, or medical imaging.[1] The benefits of screening in terms of cancer prevention, early detection and subsequent treatment must be weighed against any harms.
Universal screening or mass screening involves screening everyone, usually within a specific age group.[2] Selective screening identifies people who are known to be at higher risk of developing cancer, such as people with a family history of cancer.[2]
Screening can lead to false positive results and subsequent invasive procedures.[3] Screening can also lead to false negative results. Controversy arises when it is not clear if the benefits of screening outweigh the risks of the screening procedure, follow-up diagnostic tests and cancer treatments.
Screening tests must be effective, safe, well-tolerated with acceptably low rates of false positive and false negative results. If signs of cancer are detected, more definitive and invasive follow-up tests are performed to reach a diagnosis. Screening for cancer can lead to cancer prevention and earlier diagnosis. Early diagnosis may lead to higher rates of successful treatment and extended life. However, it may also falsely appear to increase the time to death through lead time bias or length time bias.
The following criteria are used by the UK National Screening Committee for making decisions about the effectiveness, acceptability and appropriateness of a screening test.[4]
There is general agreement in the scientific community that breast screening reduces mortality from the disease.[5]
There is some controversy however about the number of lives saved by breast screening and the number of cancers diagnosed that would not have caused any health problems in the participants' lifetime.[6]
Similarly, for breast cancer, there have recently been criticisms that breast screening programs in some countries cause more problems than they solve. This is because screening of women in the general population will result in a large number of women with false positive results which require extensive follow-up investigations to exclude cancer, leading to having a high number-to-treat (or number-to-screen) to prevent or catch a single case of breast cancer early.
The U.S. Preventive Services Task Force (USPSTF) recommends screening mammography once for every two years for all women aged 50—74, with decisions about screening younger and older women being determined by consideration of the individual's risk factors and the benefits and harms of screening. They do not recommend either breast self-examination or clinical breast examination.[7] Their recommendation is similar to the World Health Organization's, and less aggressive than most North American organizations. A 2009 Cochrane review came to slightly different conclusions with respect to breast cancer screening stating that routine mammography may do more harm than good.[8]
Cervical cancer screening via the Pap smear has the best cost-benefit profile of all the forms of cancer screening from a public health perspective as, being largely caused by a virus, it has clear risk factors (sexual contact), and the natural progression of cervical cancer is that it normally spreads slowly over a number of years therefore giving more time for the screening program to catch it early. Moreover, the test itself is easy to perform and relatively cheap.
The U.S. Preventive Services Task Force (USPSTF) strongly recommends cervical cancer screening in American women who are sexually active and have a cervix at least until the age of 65, usually every three years.[9] Their recommendation is typical of professional organizations and other government agencies in the US and Canada.
The US Preventive Services Task Force recommends screening for bowel cancer using fecal occult blood testing, sigmoidoscopy, or colonoscopy, in adults, beginning at age 50 years and continuing until age 75 years.[10]
When screening for prostate cancer, the PSA test may detect small cancers that would never become life threatening, but once detected will lead to treatment. This situation, called overdiagnosis, puts men at risk for complications from unnecessary treatment such as surgery or radiation. Follow up procedures used to diagnose prostate cancer (prostate biopsy) may cause side effects, including bleeding and infection. Prostate cancer treatment may cause incontinence (inability to control urine flow) and erectile dysfunction (erections inadequate for intercourse).[citation needed]
According to the U.S. Preventive Services Task Force (USPSTF), there is insufficient evidence to recommend for or against screening for lung cancer.[11]
Recent research suggests that screening heavy smokers may be effective.
There is insufficient evidence to recommend for or against screening for skin cancer,[12] and oral cancer.[13] Routine screening is not recommended for bladder cancer,[14] testicular cancer,[15] ovarian cancer,[16] and pancreatic cancer.[17]
According to the U.S. Preventive Services Task Force (USPSTF), there is insufficient evidence to recommend for or against screening for prostate cancer in men under 75.[18] Routine screening is not recommended for prostate cancer in men over 75.[18] Most North American medical groups recommend individualized decisions about screening, taking into consideration the risks, benefits, and the patients' personal preferences.
Use of medical imaging to search for cancer in people without clear symptoms is similarly marred with problems. There is a significant risk of detection of what has been recently called an incidentaloma - a benign lesion that may be interpreted as a malignancy and be subjected to potentially dangerous investigations.
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