Cancer screening is
an attempt to detect unsuspected cancers in an asymptomatic
population. Screening tests suitable for large numbers of
healthy people must be relatively affordable, safe, noninvasive
procedures with acceptably low rates of false positive results.
If signs of cancer are detected, more definitive and invasive
follow up tests are performed to confirm the diagnosis.
Screening for cancer can lead to earlier diagnosis in specific
cases. Early diagnosis may lead to extended life, but may also
falsely prolong the lead time to death through lead time bias or
length time bias.
A number of different screening tests have been developed for
different malignancies. Breast cancer screening can be done by
breast self-examination, though this approach was discredited by
a 2005 study in over 300,000 Chinese women. Screening for breast
cancer with mammograms has been shown to reduce the average
stage of diagnosis of breast cancer in a population. Stage of
diagnosis in a country has been shown to decrease within ten
years of introduction of mammographic screening programs.
Colorectal cancer can be detected through fecal occult blood
testing and colonoscopy, which reduces both colon cancer
incidence and mortality, presumably through the detection and
removal of pre-malignant polyps. Similarly, cervical cytology
testing (using the Pap smear) leads to the identification and
excision of precancerous lesions. Over time, such testing has
been followed by a dramatic reduction of cervical cancer
incidence and mortality. Testicular self-examination is
recommended for men beginning at the age of 15 years to detect
testicular cancer. Prostate cancer can be screened using a
digital rectal exam along with prostate specific antigen (PSA)
blood testing, though some authorities (such as the US
Preventive Services Task Force) recommend against routinely
screening all men.
Screening for cancer is controversial in cases when it is not
yet known if the test actually saves lives. The controversy
arises when it is not clear if the benefits of screening
outweigh the risks of follow-up diagnostic tests and cancer
treatments. For example: 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). 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.
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.
For these reasons, it is important that the benefits and risks
of diagnostic procedures and treatment be taken into account
when considering whether to undertake cancer screening.
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. Recent studies of CT scan-based screening for
lung cancer in smokers have had equivocal results, and
systematic screening is not recommended as of July 2007.
Randomized clinical trials of plain-film chest X-rays to screen
for lung cancer in smokers have shown no benefit for this
approach.
Canine cancer detection has shown promise, but is still in the
early stages of research.
Epidemiology >>
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Cancer
Classification
1. Nomenclature
2. Adult cancers
3. Childhood cancers
Signs and symptoms
Diagnosis
1. Investigation
2. Biopsy
Treatment
1. Surgery
2. Radiation therapy
3. Chemotherapy
4. Targeted therapies
5. Immunotherapy
6. Hormonal therapy
7. Symptom control
8. Complementary and alternative
9. Treatment trials
Prognosis
1. Emotional impact
Causes
1. Chemical carcinogens
2. Ionizing radiation &
Infectious diseases
3. Hormonal imbalances
& Immune system dysfunction
4. Heredity & Other causes
Pathophysiology
1. Epigenetics
2. Oncogenes
3. Tumor suppressor genes
4. Cancer cell biology
4.1 Clonal evolution
4.2 Biological properties of cancer cells
Prevention
1. Modifiable ("lifestyle") risk factors
2. Diet
3. Vitamins
4. Chemoprevention
5. Genetic testing
6. Vaccination
7. Screening
Epidemiology
History
Research |
