The term ‘screening’ is derived from the verb ‘to screen’ and means ‘to guard’ or ‘to filter’. The
aim of a nationwide screening programme is to ‘filter’ an in principle healthy population in
order to detect those with a disease or condition at an early stage, before the occurrence of
any signs or symptoms. Actively looking for the early stages of a disease or condition is classified
as secondary prevention. Additionally, primary prevention strategies intend to avoid the
development of the disease and tertiary prevention aims to reduce the negative impact of
established disease by restoring function and reducing disease-related complications.
The development of a malignancy is a multistep process: at some point in time the first
cancer cells develop and will start to divide in an uncontrolled way ultimately resulting in
a tumour. Growth is local at first but then continues into the surrounding tissues and eventually
metastasizes, ultimately leading to the individuals’ death. At some stage during this
process, the individual generally seeks medical advice for their newly-developed symptoms.
Subsequently, further investigations are carried out and the diagnosis of ‘cancer’ is made.
Between the start of the uncontrolled division of the first cancer cells and manifestation of
symptoms, there may be a moment at which the tumour is large enough to be detected by
a screening test. The aim of screening is therefore to bring forward the time of diagnosis
before the stage at which the first signs and symptoms of the disease come to light, the
so-called lead time. Detection at an early stage is associated with less intensive treatment
and a better outcome. Depending on the disease and test characteristics, screening may in
some instances also detect the premalignant lesions that manifest themselves prior to the
invasive stage.http://repub.eur.nl/res/pub/32158/120418_Roon%2C%20Aafke%20Hendrikje%20Christina%20van.pdf
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