Screening should have a clear, measurable health target.
It is important to have scientific evidence of the effect of screening on the target, i.e. to know its effectiveness.
Effectiveness is usually measured by reduction of mortality from the neoplastic disease.
Whenever a new screening programme is started (or a current programme is changed), its relevance for health care in the country can be examined.
Notice that this article is based on and in several occasions describes population screening programmes applied in Finland. Important country-specific differences may apply. Consult national documentation for details concerning your country.
Benefits and harms
Cancer screening aims at diagnosing cancers at an early stage when curative treatment is possible and death from cancer can be avoided. Its general aim is to increase health either by preventing death or by improving the quality of life.
In addition, cancer screening may have other benefits. It may reduce human suffering, for instance, by making it possible to avoid adjuvant therapy. For society, early treatment of cancer brings savings through shorter periods of treatment and by often making aggressive and expensive treatment unnecessary.
However, screening also has its harms. On the one hand, false positive screening results lead to needless further examinations in healthy people while on the other latent cancer may remain undetected because of false normal findings.
In a good screening programme, benefits and harms are in balance and there is sufficient research-based data available.
Screening programmes recommended to be included in a public health policy
Cervical cancer
The evidence on the benefits of screening is based on large population-level screening programmes.
By screening, it is possible to reduce the incidence of cancers and of cancer mortality by as much as 80%.
In Finland, screening is done by cervical exfoliative cytology tests performed every 5 years from age 30 to age 65.
In some municipalities, women aged 25 may also be screened.
Either the traditional Pap smear or an HPV test can be used for screening.
The HPV test leads to more diagnosis of precancerous lesions and hence overtreatment, especially in young women.
In Finland, girls of 12-15 years have been vaccinated against HPV infection since 2013. Boys were included in the programme in 2020.
Evidence on the cancer-preventing effect of HPV vaccination is based on combining knowledge of cancer and severe precancerous lesions.
Vaccinated age groups will not reach the lower age limit of the Finnish national screening programme until 2030s.
In addition, for decades to come, there will be a large female population not covered by any protective effect of the vaccination.
In young women, HPV infections often clear spontaneously. Therefore, the younger the screened women the larger the relative share of overdiagnosis (of non-progressive precancerous lesions).
To balance benefits and harms, exfoliative cytology testing should be avoided outside the screening programme in healthy, asymptomatic (young) women, and the resources should be used for the organized screening programme.
In Finland, when the national population screening commenced in 1987, the evidence for its benefits was originally based on randomized screening trials. Women aged 50-69 years are screened every two years.
The screening programme reduces breast cancer mortality by a fifth in those invited for screening and by a third in those participating in screening compared to the situation without screening.
This means that screening prevents about 100 breast cancer deaths per year.
Mammography is used as the screening test
Young women have a lot of glandular tissue appearing dense in mammography.
Dense breast tissue reduces the effectiveness of mammography screening since the tissue may hide some cancers.
With age and decreased hormone production, the amount of glandular tissue is reduced, but it may be increased by menopausal hormone replacement therapy, for example.
If the result remains unclear, the test can be complemented by other methods.
As the screening of women below 50 is less useful than of those over 50, the recommendation concerning lowering the screening age limit to 45 is conditional.
A conditional recommendation has been made also concerning the extension of screening from 70 to 74 years.
The evidence for the benefits of screening is based on randomized screening trials. According to these, mortality in colorectal cancer is reduced by 10-40%.
In men, screening has decreased cancer mortality more, on an average, than in women.
In randomized trials, once in a lifetime sigmoidoscopy at the age of about 50-64 decreased mortality in colorectal cancer by 20-31%.
The effectiveness of colonoscopy screening is being examined in four randomized trials.
Based on screening trials, colonoscopy is expected to reduce mortality more than sigmoidoscopy.
However, in routine health care, the effect on mortality will probably remain less.
Colonoscopy, unlike faecal blood testing, is an invasive procedure and associated with possible harms.
The European Union recommends screening based on a faecal blood test for men and women of 50-74 years every 2 years.
In Finland, screening for colorectal cancer with a stool guaiac test was in use in 2004-2016. Municipalities were able to participate on a voluntary basis.
After an average follow-up of slightly less than 5 years, no change in mortality had been found between those invited for screening and their controls.
Based on improved survival, organized screening was found to have indirect benefits also for the non-invited population, resulting from the improved patient paths.
Screening began again in Finland as a new pilot in spring 2019.
Screening will gradually expand to cover men and women between 56 and 74.
The screening test is a quantitative immunochemical faecal blood test widely used in other European countries, as well.
In the national programme, cut-off values of the test are the same for men and women.
A positive screening test result is confirmed with colonoscopy.
The effectiveness of screening is closely monitored, with particular attention paid to differences between women and men.
The aim is to establish an effective screening programme for both women and men.
Screening programmes that have a known effect on mortality but not yet recommended to be included in a public health policy
Organized screening based on PSA tests reduces mortality from prostatic cancer by about 20% in men over 55 years of age.
Elderly men often have a latent prostate cancer that produces no symptoms and does not shorten the life expectancy. Detecting such cancers increases overt morbidity, and the adverse effects of their treatment decrease the quality of life.
The common habit of routinely determining PSA as a part of clinical practice, e.g. in occupational health care, should be discouraged.
For the time being, there are no grounds for starting an organized population screening programme in Finland, particularly because treatments impair the quality of life. A new trial (ProScreen http://pubmed.ncbi.nlm.nih.gov/34958531/) is underway and results will be available in a few years.
CT-based screening for lung cancer has reduced the mortality of patients with a long history of smoking by 15-20%.
However, the share of false positive test results and the price per additional year of life gained have been high.
Several small randomized population-based screening trials have been performed in Europe. There have been essentially fewer false positive findings on imaging, and a smoking cessation intervention has been used in both trial and control populations.
The initial results from the largest trial suggest that screening reduces mortality in lung cancer.
It has been estimated that a smoking cessation intervention might have a more long-term and stronger effect on mortality in lung cancer than screening.
Challenges include identification of target population (with long history of smoking) as well as availability of adequate resources (CT scanning device(s) and personnel for interpreting results), and consequently the practical implementation and feasibility must be investigated before deciding on the screening.
Screening programmes not recommended to be included in a public health policy
Ovarian cancer
The effect of screening on ovarian cancer mortality has been studied in two large randomized trials.
Based on the results, screening does not reduce ovarian cancer mortality but it may have significant disadvantages.
For these reasons, screening is not recommended.
Gastric cancer
Eradication therapy of Helicobacter infections has reduced the incidence of gastric cancer by about 30-35% in countries where the risk of gastric cancer is high on the population level.
In countries with a low risk of gastric cancer, such as Finland, population-level screening is not indicated.
There are screening tests available for the detection of cancers such as cancer of the oral cavity, skin melanoma, cancer of the corpus uteri, liver cancer and several others.
However, they are not recommended for routine screening because their effect on mortality has not been studied.
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