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Cancer Screening

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What is a screening test?

Cancer screeningA screening test is any investigative method that can be applied to a seemingly healthy patient for the purposes of diagnosing underlying conditions that may have otherwise gone unnoticed. The purpose of such a test is to allow for treatment of these conditions to be started as soon as possible, leading to better outcomes. A screening test is not meant to give a definite answer about a diagnosis, but rather is just there to indicate if there should be further tests. Usually a screening test will take place when a patient presents to their GP for another purpose. This is because the purpose of screening is to pick up people who are not yet showing symptoms of the disease rather than waiting until they show symptoms. There are some instances however, where formal screening may be organised centrally by the health department.

Screening for certain cancers in people without any symptoms is an excellent public health initiative that each year saves many lives. However, in some cases there is little evidence that screening improves the quality of life or chance of survival for people diagnosed with the condition. Also, some screening tests can lead to further, more invasive, test that can have some complications associated with them. The Western Australian Clinical Oncology Group and the Australian Cancer Council have looked at all the evidence surrounding these screening tests and come up with some recommendations for screening specific cancers.


What makes a good screening test?

The reason some screening tests are not used is because no test is perfect; especially ones that are designed to be as quick, cheap and easy as is necessary to be a screening test. To help explain this idea, here are a few examples of the terms used to describe tests and work out how suitable they are:

  • Sensitivity: This is the percentage of people who have the disease that will be picked up by the test. The higher this is the better, as then it is less likely the test will not pick up someone who actually has the disease.
  • Specificity: This shows how good a test is at showing that a person does not have a disease. Sometimes a test can come back saying that there is no disease, when actually there is; however, the higher the specificity, the lower the chances are of this occurring.
  • Positive predictive value: This is the percentage of times a person who the test says has the disease, actually does have it. Sometimes a ‘false-positive’ result can occur, where the test shows that the person has the disease when they actually do not. The higher the positive predictive value of a test, the lower the chance is of this occurring.
  • Negative predictive value: This is the percentage of times when if a person does not have the disease, the test will show that correctly. The higher the better, as the higher it is the more likely a negative test result is to be accurate.
  • Acceptability: This is not a statistical term, but rather simply pointing out that for a screening test to be good it has to not only be statistically sound (in the ways described above) but also be cheap, quick, easy to do and not too unpleasant for the patient. If this is not the case, then no one will want to do the screening test and so the who effort will be wasted.


Which diseases are good for screening?

Cancer screeningSome diseases are good ones to screen for, and others are not. Basically, there are a couple of things about a disease that make it a good candidate for screening tests:

  • The disease, and how it progresses, should be well understood. It should also have a long time when it is just beginning to become a problem but is not yet spreading or causing major trouble, as this gives a good window for when screening can diagnose it.
  • The disease should be common, and also associated with a high level of mortality (death) or morbidity (loss of quality of life). It is a waste of resources to check for a disease that only a tiny fraction of people will get because it will not find very much but will cost a lot of time, effort and money that could be put elsewhere.

There should also be good treatment available for the disease, otherwise what is the point in looking for it? A screening test should be to look for diseases which can have something done about them.The testing should be acceptable, safe and relatively cheap.


Screening guidelines

Cancer screeningDeciding which diseases should be screened for requires a lot of research, and so often it falls to some big organisations to decide how, when and what diseases to screen for. They do this through the publication of ‘screening guidelines‘ that detail all the information about screening for diseases. Each of the groups do not always come to exactly the same conclusion, but are often very similar. Two major guidelines in Australia are the one produced by the Cancer Council, and one produced by the Western Australian Clinical Oncology Group (WACOG). For the most part these are the same, however any differences will be pointed out in the article.


Breast cancer

WACOG (Strongly recommended with good evidence)

Mammography is recommended for the screening of breast cancer every two years for average risk women between the ages of 50 and 69. Some women are said to be at a moderately increased risk compared to the rest of the population because they have:

  • One or two first-degree relatives diagnosed with breast cancer before the age of 50 OR
  • Two first or second-degree relatives on the same side of the family, diagnosed with breast or ovarian cancer.

For these women the guidelines say that they should present for the usual screening, once every two years after 50; however, additional surveillance may be recommended by your doctor. Some women are said to be at an even higher risk of breast cancer, due to:

  • Breast or ovarian cancer diagnosed in three or more first or second-degree relatives on the same side of the family; or
  • Two or more first- or second-degree relatives on the side of the family diagnosed with breast or ovarian cancer, plus one or more of the following features (on the same side of the family):
    • A breast cancer in both breasts
    • Onset of breast cancer before the age of 40
    • Onset of ovarian cancer before the age of 50
    • Breast and ovarian cancer in one individual
    • Jewish ancestry
    • Breast cancer in a male relative
  • One first of second-degree relative diagnosed with breast cancer at age 45 years or younger, plus another first- or second-degree relative on the same side of the family with bone or soft tissue sarcoma at age 45 or younger
  • A genetic mutation that can predispose some women to breast cancer.

For these women, screening guidelines remain controversial, and so it is recommended that they attend a specialised cancer or genetic service for advice.

Cancer Council Australia

The Cancer Council guidelines are slightly different, and while the recommend the same screening process as the WACOG, they also advise being ‘breast aware’ and encouraging women to familiarise themselves with the normal look and feel of their breasts. They also recommend seeing a doctor immediately if there is any noticeable change in the breast tissue. It also points out that while screening for women between the ages of 40 and 50 is not strongly recommended due to the difficulty in detecting cancers on mammograms, they still have free access to BreastScreen Australia if they should wish.

Breast cancerFor more information on breast cancer, types of breast cancer and its investigations and treatments, as well as some useful videos, see Breast Cancer.


Cervical cancer

WACOG (Strongly recommended with good evidence)

Screening for cervical cancer through the use of a Pap smear should be commenced between the ages of 18-20 or within two years of sexual intercourse, whichever is later. In some cases it may be appropriate to begin screening at an earlier stage. These should be conducted every two years. Pap smears can be stopped when the woman reaches 70 and has had two normal smears within the last five years; however, if the woman is over 70 and has never had a Pap smear, or requests a Pap smear, then they should be screened. In women who have had a hysterectomy for non-cancer reasons, and who have never had an abnormal smear, then no further vaginal vault Pap smears are required. If the hysterectomy was performed for pre-cancerous lesions however, then a vaginal vault smear should be conducted every year for five years, and may then return to one smear every two years.


Cancer Council Australia

The Cancer Council recommends that for all women aged between 18 and 70 who have ever been sexually active, a Pap test should be conducted every two years as part of the National Cervical Screening Program. They also point out that current evidence is suggesting that maybe doing a Pap test every three years instead of two would be suitable, and so suggest doctors consider this regime instead.


Colorectal cancer

WACOG (Strongly recommended with good evidence)

Cancer screeningThe screening for colorectal cancers is different for various groups depending on how ‘at risk’ they are. Some people have been shown in studies to have a higher risk than others and this affects how they will be screened. In normal, low-risk, people who are asymptomatic and with no family history it is recommended that faecal occult blood testing be performed from the age of 50. This should be done as a series of three serial stools, at least every second year. These are usually collected by the patient, and can require some modification to the diet for a few days to remove other sources of blood as that can confuse the test. It is also acceptable to offer flexible sigmoidoscopy (where a camera is inserted into the last section of the bowel to look for abnormalities) as a screening method on a five-yearly basis. The Australian government has recently introduced a National Bowel Cancer Screening Program offering free faecal occult blood testing to eligible participants. For more information, see screening for bowel cancer. Some people are at a higher risk, due to:

  • Having one first-degree relative with colorectal cancer diagnosed before the age of 55 or
  • Having two first or second-degree relatives on the same side of the family with colorectal cancer diagnosed at any age

In these people, it is recommended that they be referred for a colonoscopy (a longer camera than in a sigmoidoscopy, looking for abnormalities in the entire large bowel) every five years from age 50, or 10 years younger than the age of the earliest diagnosis of colorectal cancer in the family. If colonoscopy is not available then a flexible sigmoidoscopy is a reasonable alternative. Faecal occult blood tests should be considered in the years in between these.

Some other people are at an even higher risk; and for these people management should be with the support of clinical genetics and cancer genetics services, with referral at an early age. The features of high-risk individuals are:

  • Three or more first or second degree relatives on the same side of the family, diagnosed with colorectal cancer
  • Two or more first or second degree relatives on the same side of the family diagnosed with colorectal cancer, including any of the following high-risk features:
    • Multiple colorectal cancers in one person
    • Colorectal cancer before the age of 50
    • At least one relative with endometrial or ovarian cancer
  • At least one first or second degree relative with colorectal cancer, with a large number of adenomas (small growths) throughout the large bowel
  • Someone in the family with a high-risk genetic mutation


Cancer Council Australia

The Cancer Council recommends that everyone over the age of 50 years (and without a strong family history, as discussed above), should be encouraged to undergo a FOBT every two years and if blood is seen then a follow-up investigation (commonly a colonoscopy) is needed. They also recommend that people with the following symptoms present to their doctor for investigation:

  • Bleeding from the back passage of sign of blood in a bowel motion
  • An unexplained and persistent change in bowel actions
  • Unexplained tiredness
  • Lower abdominal pain or a persistent feeling of fullness

People with a strong family history should discuss screening with their doctors.


Lung cancer

WACOG (Insufficient evidence)

While there are possible methods for screening of lung cancer, studies have not shown that they help to improve the quality of life or life expectancy of those who are diagnosed. For this reason it is not recommended that doctors routinely screen for lung cancers, even in high-risk people (such as smokers and people exposed to asbestos) because there is no advantage to doing so.


Melanoma

WACOG (Insufficient evidence)

Currently, there is no evidence that shows screening people without symptoms for melanomas helps to improve life expectancy. This is currently an area of heated research, but as of this time it is not a recommended practice. However, in populations with higher risk (such as those with light skin, tendency to burn, freckling, atypical moles, having more than 50 moles on the body, a family history of melanoma or a past history of melanoma or non-melanoma skin cancer), annual screening is recommended.


Ovarian cancer

WACOG(Insufficient evidence)

Routine screening of women for ovarian cancer is not recommended. The problem is that while there are several tests that theoretically could be used for screening, none of them are particularly sensitive or specific in asymptomatic women (they will miss a lot of women who do have the disease, while also wrongly diagnosing women who do not have it). In women who are at a higher risk (classified as a strong family history of breast and/or ovarian cancer OR a strong family history of colon cancer) then blood tests can be done, and an ultrasound through the vagina an into the pelvis can be done every few years.


Prostate cancer

WACOG and Cancer Council Australia (Insufficient evidence)

Screening for prostate cancer is still a topic of debate among many health professionals as there are currently no studies evaluating the impact of screening on quality of life and long-term survival. Screening methods include examining the prostate with a finger inserted into the rectum, a blood test called a PSA (prostate-specific antigen) and trans-rectal ultrasound. While there may be some evidence that detection improves health outcomes, screening can be associated with some possible harms. These are usually associated with diagnosing conditions that would not have caused much of a problem and leading to other, more invasive, investigations that can have complications. For this reason, while it is currently not recommended, but this position may change over the next few years as more information comes out.

Prostate cancerFor more information on prostate cancer, including diagnoses, types of treatments, and some useful tools, videos and animations, see Prostate Cancer.


Testicular cancer

WACOG and Cancer Council Australia (Insufficient evidence)

With regards to screening for testicular cancer, there is simply not enough research to either recommend, or recommend against, screening. The only viable screening method is examination, either by a doctor or by the patient; currently however, there is nothing to indicate whether or not this practice improves rates of morbidity and mortality. While monthly self-examination is sometimes recommended, there is no evidence to whether this improves outcomes or not.

References

  1. ‘Cervical Cancer Screening Position Statement’ [online], The Cancer Council Australia, Available at: http://www.cancer.org.au/ documents/ Cervical_cancer_screening_pos_statement_2006.pdf (last accessed: 31/05/2007)
  2. ‘Early Detection of Breast Cancer’ [online], The Cancer Council Australia, Available at: http://www.cancer.org.au/ documents/ Early_detection_breast_cancer_%20MAY04.pdf (last accessed: 31/05/2007)
  3. ‘NHMRC Cervical Guidelines’ [online], National Health and Medical Research Council, 16/03/2007. Available at: http://www.cancerscreening.gov.au/ internet/ screening/ publishing.nsf/ Content/ guide (last accessed: 22/05/2007)
  4. ‘Prostate Cancer Screening Position Statement’ [online], The Cancer Council Australia, Available at: http://www.cancer.org.au/ documents/ Pos_State_Prostate_cancer_screening_MAY2005.pdf (last accessed: 31/05/2007)
  5. ‘Screening for Various Cancers’ [online], World Health Organisation, Available at: http://www.who.int/ cancer/ detection/ variouscancer/ en/ index.html (last accessed: 20/05/2007)
  6. ‘Testicular Cancer Position Statement’ [online], The Cancer Council Australia, Available at: http://www.cancer.org.au/ documents/ Pos_Statement_Testicular_cancer_DEC04.pdf (last accessed: 31/05/2007)
  7. Fritschi, L. Recommendations for Screening for Specific Cancers: Guidelines for General Practitioners (Second Edition). Perth: Western Australian Clinical Oncology Group; 2005.
  8. Greenberg, RS, Daniels, SR, Flanders, D, et al. Medical Epidemiology (Third ed). 2001, Lang Medical Books/McGraw-Hill: New York.
  9. Murtagh, J. General Practice (Third ed). 2005, Mcgraw-Hill: Sydney.
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Dates

Posted On: 28 December, 2005
Modified On: 31 August, 2015

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