Cancer: early detection

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What is it about ?

Screening involves finding a condition or the risk of developing a condition in a person who has no symptoms. The goal of screening is to be able to identify and treat the condition at an early stage, before it reaches a stage that is more difficult or impossible to treat. In other words, screening aims to find malignant conditions or lesions at a time when a cure is still possible.

There are 2 types of screening: opportunistic screening and systematic screening.

  • In the opportunistic screening, a condition is sought in patients who consult the doctor for other complaints. Thus, a doctor can, for example, offer screening for bowel cancer to people over the age of 50 who come to have their blood pressure checked.
  • In the systematic screening, a whole population group is invited to take a specific exam. All women between the ages of 50 and 69, for example, are encouraged to have a mammogram.

Advantages and disadvantages of screening

At first glance, screening only seems to have advantages. Conditions are detected before they get worse and cause symptoms. But there are also downsides.

  • A big drawback is linked to the impossibility of knowing in advance how certain cancers will evolve. In men, some prostate cancers are ‘dormant’. In other words, they don’t grow and don’t get bigger. Other prostate cancers, on the other hand, grow, but very slowly, sometimes over a period of 15 years. Finding these cases will also sound the alarm and sometimes lead to aggressive treatment, such as removal of the prostate. A number of men will (unnecessarily) experience negative consequences, such as urinary incontinence and impotence.
  • Screening is expensive, especially if you want to subject an entire population to it. In addition, many conditions are quite rare, so the chances of detecting them are relatively low. A fair balance must therefore be found between an acceptable cost and the expected result. To do this, the target group must be defined with great precision. 20-year-old women should therefore not be routinely screened for breast cancer, as the disease hardly ever strikes at that age. Rather, the target group here will be all women aged 50 to 69.
  • In addition, there are no quality tests for all types of cancer. The ideal test is one which always gives a positive result in the presence of the disease and which always gives a negative result in the absence of the disease. Unfortunately, the ideal test does not exist. Sometimes false-positive and false-negative results are still possible. A false positive indicates abnormalities that do not exist, while a false negative gives a normal result when the person does have early cancer. A good test should therefore give as few false results as possible.

In summary :

  • A good screening program should provide sufficient health benefit: mortality from the disease should decrease and quality of life should increase.
  • A quality test should be available at an acceptable price.
  • A screening test should have as few negative effects as possible.
  • There must also be treatment for the type of cancer in question, the side effects of which are acceptable.

Cancers for which screening is recommended

In Belgium, the public authorities organize systematic screening programs for cervical cancer, breast cancer and colorectal cancer.

For a national screening program to be set up for a specific condition, a number of criteria (Wilson & Jungner) must be met:

  • it is a serious health problem,
  • we know how the disease evolves over time,
  • there is a reliable quality screening test,
  • this test is acceptable to people (it should not be too painful or result in incapacity for work, for example),
  • the cost of the test is acceptable to the company,
  • there is an effective treatment.

Cervical cancer

Screening for cervical cancer involves taking a smear from the cervix. The cervix is ​​the transition zone between the uterus and the vagina; it is coated with cells that are different from the cells of the uterus. These cells can become malignant. In many cases, this development occurs under the influence of the human papillomavirus (HPV), a sexually transmitted virus.

Screening for cervical cancer is offered every 3 years to all women aged 25 to 65, except women who no longer have a uterus and women who have never yet had sex. Screening is also recommended for women who are vaccinated against HPV.

In Belgium, the test used detects both cancer cells and the HPV virus. It can detect up to 80% of cervical cancers at an early stage. The main drawback is that this test can detect abnormal cells, which may become malignant (these are also called ‘precancerous cells’), but the majority of these abnormal cells return to normal on their own and therefore should not require treatment. processing. Since it is not known whether these abnormal cells will return to normal or become cancerous, it is proposed to treat them. As a result, a number of women are likely to be treated unnecessarily for cancer that will not develop. In addition, some types of cancer develop and grow so slowly that they would not have caused concern during the patient’s lifetime. Again, since it is not always possible to differentiate between “slow” and “fast” cancers, it is often suggested that they all be treated.

The ideal time between two smears is not clearly known: 2, 3 or even 5 years. According to some studies, detection of the HPV virus alone would be sufficient. This is, moreover, the choice made in the national screening program in the Netherlands.

Breast cancer

A mammogram is recommended every 2 years for:

  • women aged 50 to 69;
  • women aged 40 to 50 who are at increased risk of breast cancer (due to a family history, for example);
  • women aged 70 to 74 who are still in good physical condition.

During a mammogram, 2 ‘photos’ (x-rays) of each breast are taken: 1 from the side and 1 from top to bottom. If an abnormality is found, an ultrasound is done and sometimes an MRI.

The main drawback is that, although the technique has improved considerably, the examination still gives 2 to 4% of false-positive results: the test therefore indicates an anomaly while there is no question of breast cancer. breast. As a result, a number of women are treated unnecessarily.

There is also a (very low) risk associated with the use of rays during the examination. It is estimated that 1 to 10 in 100,000 screened women develop cancer as a result of the radiation.

Breast cancer screening reduces breast cancer deaths by 30%.

Colorectal cancer

Screening for colorectal cancer can be done in 2 ways: by looking for blood that cannot be seen with the naked eye (occult blood) in the stool and by a colonoscopy, an endoscopy of the large intestine.

  • Check for blood, invisible to the naked eye, in the stool. A small stool sample is sufficient. The test proposal is sent every 2 years to all people aged 50 to 74.
  • The colonoscopy is an expensive and invasive examination, which must be performed in the hospital. It is therefore reserved for people who have tested positive on the FOBT test or for people who have an increased risk of bowel cancer.

One of the disadvantages is the large number of causes that can explain the presence of blood in the stool. So this is not always a sign of cancer.

Thanks to screening, deaths from colorectal cancer are said to have fallen by 15%.

Cancers for which screening is possible, but not systematically implemented

Prostate cancer

Among men over 60, screening is based on measuring the level of PSA (Prostate Specific Antigen) in the blood. An increased PSA can indicate prostate cancer, but often has another cause, such as inflammation or a benign enlargement of the prostate (benign prostatic hypertrophy).

Screening for prostate cancer would reduce the death rate by about 20%. But the big problem is that it leads to unnecessary treatments. A large number of men suffer from ‘latent’ or ‘dormant’ prostate cancer, a type of cancer which will never cause problems, which will never develop metastases and which has no influence on the prostate. lifetime. However, their diagnosis will almost always lead to aggressive treatment, with side effects such as incontinence and impotence. Our country does not organize systematic screening, which is moreover not recommended.

Lung cancer

Screening for lung cancer requires a CT scan of the lungs, an expensive and risky procedure due to exposure to (potentially harmful) x-rays. The reduction in the lung cancer death rate recorded by screening could be as much as 20%. In Belgium, no project currently aims to set up systematic screening for lack of solid scientific evidence.

Cancers for which systematic screening is not currently recommended

These include, in particular, cancer of the skin, stomach, throat, liver, etc. For these types of cancer, it is not clear what effect routine screening has on the death rate.

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Source

Foreign clinical practice guide ‘Public health policy on cancer screening’ (2000), updated on 14.06.2017 and adapted to the Belgian context on 14.04.2019 – ebpracticenet