Colorectal Cancer Screening by Means of Faecal Immunochemical Testing (FIT)

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.

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