Figure 1. Mechanisms for Benefits and Harms of Cancer Screening on Longevity of Life.

The horizontal arrows illustrate 4 individuals who underwent screening. Arrows pointing right: 2 individuals who experienced screening benefit and live longer by early cancer detection and cure. Arrows pointing left: 2 individuals who experienced harm related to screening and died earlier than those without screening. The blue circle indicates population longevity effect of screening, which was calculated as all individual benefits minus all individual harms.

^aHarms of screening include perforation or bleeding during sigmoidoscopy and of diagnostics and treatment after screening, such as surgery, radiotherapy, and chemotherapy.