Cancer screening

Recommended screening for breast, cervical, colorectal, and lung cancer reduces cancer specific mortality.

Cancer screening aims to detect cancer before symptoms appear.

This may involve blood tests, urine tests, DNA tests, other tests, or medical imaging.

The benefits of screening: cancer prevention, early detection and subsequent treatment, must be weighed against any harms.

Universal screening (mass screening) or population screening, involves screening everyone, usually within a specific age group.

Selective screening identifies people who are known to be at higher risk of developing cancer, such as people with a family history of cancer.

Screening can lead to false positive results and subsequent invasive procedures.

Screening can also lead to false negative results, where an existing cancer is missed. 

Screening tests must be effective, safe, well tolerated with acceptably low rates of false positive and false negative results. 

Screening for cancer is controversial when it is not yet known if the test actually saves lives.

Cancer screening is not indicated unless life expectancy is greater than five years and the benefit is uncertain over the age of 70.

Factors to be considered to determine whether the benefits of screening outweigh the risks and the costs of screening:

Possible harms from the screening test: X-ray images exposingthe body to potentially harmful ionizing radiation. 

There is a small chance that the radiation in the test could cause a new cancer in a healthy person. 

Screening mammography, used to detect breast cancer, is not recommended to men or to young women because they are more likely to be harmed by the test than to benefit from it. 

A test that has high potential harms is only recommended when the benefits are also high.

The likelihood of the test correctly identifying cancer.

All cancer screening tests produce both false positives and false negatives: most produce more false positives. 

A positive predictive value is a calculation of the likelihood that a positive test result actually represents cancer in a given individual, based on the results of people with similar risk factors.

Screening is not normally useful for rare cancers. 

It is rarely done for young people, since cancer is largely a disease found in people over the age of 50. 

Countries often focus their screening recommendations on the major forms of treatable cancer found in their population: United States recommends screening for colon cancer; Japan recommends screening for stomach cancer

Screening recommendations depend on the individual’s risk.

High-risk people receive earlier and more frequent screening than low-risk people.

If a screening test is positive, further diagnostic testing is normally done, such as a biopsy of the tissue. 

If the test produces many false positives, then many people will undergo needless medical procedures, some of which may be dangerous.

Screening is discouraged if no effective treatment is available.

The diagnosis of a fatal disease may produce significant mental and emotional harms. 

When treatment is available, sometimes early detection does not improve the outcome. 

If the treatment result is the same as if the screening had not been done, the screening program increases the length of time the person lived with the knowledge that he had cancer: lead-time bias. 

A useful screening program reduces the number of years of potential life lost and disability-adjusted life years lost.

Diagnosis of a cancer in a person who will never be harmed by the cancer is called overdiagnosis. 

Overdiagnosis is most common among older people with slow-growing cancers: overdiagnosis is common for breast and prostate cancer.

If a screening test is too burdensome, requiring too much time, too much pain, or culturally unacceptable behaviors, then people will refuse to participate.

The total cost of the screening program to the healthcare system: ordering the test, performing the test, reporting the results, and biopsies for suspicious results, but not usually the costs to the individual.

The extent to which a cancer is treatable is a major consideration in cancer screening if a person has a low life expectancy or otherwise is in the end stages of a chronic condition, then such a patient may have a better life by ignoring the cancer even if one were found. 

If the diagnosis of cancer would not result in a change in care then cancer screening would not likely result in a positive outcome. 

Overdiagnosis in this case occurs, for example, in patients with end-stage renal disease and organizations recommend against cancer screening for such patients.

People with mental illnesses are nearly 25% less likely to attend cancer screening appointments. 

Women with schizophrenia are the least likely to be screened. 

Patients with common mood disorders such as anxiety and depression are less likely to be screened than the general population: people with mental illnesses tend to die 15–20 years earlier than the general population.

People from minority ethnic communities are less likely to attend cancer screenings.

Common cancer screening programs include breast cancer, cervical cancer, colorectal cancer, prostate cancer, lung cancer

It is generally agreed that general screening of large groups for pancreatic cancer is not at present likely to be effective.

Some recommend regular screening with endoscopic ultrasound and MRI/CT imaging for those at high risk from inherited genetics.

For screening, special CT scanning procedures may be used, such as multiphase CT scan.

The US Preventive Services Task Force (USPSTF) has found that evidence was insufficient to determine the balance of benefits and harms of screening for oral cancer in adults without symptoms.

It is, however recommended that adults over 20 years who have periodic health examinations and the oral cavity examined for cancer.

There is insufficient evidence to recommend for or against screening for skin cancer, and bladder cancer.

Routine screening is not recommended for testicular cancer and ovarian cancer.

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