One in Four Dies of Cancer. Questions About the Epidemiology of Malignant Tumours.

Cancer is the second leading cause of death globally. Malignant tumours are responsible for about 9.6 million deaths in 2018 (Ritchie H (2019) How many people in the world die from cancer? https://ourworldindata.org/how-many-people-in-the-world-die-from-cancer ). Worldwide, about 1 in 6 deaths is due to cancer. This confronts researches with the question of their origin and doctors with treatment options. It is common sense that great efforts should be done in order to reduce the number of cancer-specific deaths. In recent years, in lots of countries a variety of cancer screening programs have been developed, investigated and improved. The basic idea of this approach seems to be quite simple: Tumours will be detected at a very early stage when patients do not yet feel clinical symptoms. Thus, using an appropriate therapy, progression of the disease can be prevented and, concerning a whole population, disease-specific mortality should be reduced. Actually, after the introduction of screening programs, an increasing number of new cancer cases can be observed associated with an apparent reduction of the case fatality rate (i.e. the proportion of deaths due to cancer). Partly, the increasing number of cancers may be explained by the fact that people have a higher life expectancy. Under this aspect, the decreased case fatality rate could be considered as a success which may be attributed to screening efforts. However, there is still insufficient evidence affirming benefits of screening programs for crucial outcomes, i.e. all-cause mortality. In this narrative review, the phenomenon that probabilities and risks are rather often interpreted in an inadmissible way will be described. Furthermore, conceptual issues and inconsistencies between evidence and opinion about screening will be explored.