Basic Theory of Screening for Short-Term Evaluation of Population-Based Screening for Colorectal Cancer

Abstract

Screening plays an important role in early detection of colorectal cancer (CRC) with an available screening tool followed by appropriate treatments and therapies to reach the ultimate goal of reducing colorectal cancer mortality given a progressive property of the evolution of CRC in the absence of screening. However, whether the effectiveness of screening in reducing mortality is highly dependent on when the uptake of screening is intervened at early or late time point of the duration between preclinical detectable phase (PCDP) and clinical phase (CP) estimated by the mean sojourn time (MST) dwelling at PCDP. The MST is cardinal estimate for the short-term evaluation of the quality control over the occurrence of interval cancers (cancers diagnosed between screens), a proxy for long-term effectiveness of population-based organized service screening.

In this chapter, we first introduce the basic screening theory from three-state evolution of CRC in terms of MST in relation to the time of screening. We proposed two methods to estimate the MST. The first prevalence pool method is illustrated with the UK randomized controlled trial on guaiac fecal occult blood test (gFOBT)-based screening program. The second day method, interval cancers as a percentage of the expected incidence with adjustment for MST, is revisited and modified to evaluate population-based organized service screening program in terms of test sensitivity, positive predictive value, and negative predictive value. Such a Day method is illustrated with the Taiwanese Colorectal Cancer Screening Programs with the screening tool of faecal immunochemical test (FIT). The proposed methodology on MST with a sound theory of screening is feasible for a short-term evaluation of population-based organized service screening to monitor the quality of service screening program and also reveal the odds of achieving long-term benefit of population-based screening for CRC.