Important Influences on Effectiveness and Costs to Be Considered in the Evaluation of Cancer Screening

Trials of cancer screening are designed to give an answer to the question of whether screening is effective, in particular in reducing cancer mortality. The main result of such a design is presented as a relative risk of dying from cancer in the study group (invited to screening) as compared to the control group (not invited). This relative risk is often treated as a constant which does not depend on the particular screening situation (Elwood el at., 1993). But it has been shown that the cost-effectiveness ratio can differ strongly with economic context (Brown and Fintor, 1993). Besides the economic context, effectiveness and costs of screening also strongly depend on several other aspects of the screening situation. In this chapter we describe such aspects and give some examples of quantification of their influence as estimated with the aid of the MISCAN simulation package (Habbema et al., 1985; Loeve et al., 1999) with examples mainly from models of breast cancer screening (van Oortmarssen et al., 1990; de Koning et al., 1991; de Koning et al., 1995), because international interest has focused strongly on screening for cancer of this site. Other examples are mostly from models of cervical cancer screening (van Ballegooijen et al., 1990; Koopmanschap et al., 1990; van Ballegooijen et al., 1992a; van Ballegooijen et al., 1995; van Ballegooijen et al., 1997). The authors models on prostate cancer screening (Boer et al., 1997) and colorectal cancer screening (Loeve et al., 1999) are not yet suitable for public health decision support because the evidence on efficacy is too preliminary for prostate cancer screening in general and for colorectal cancer screening if any screening modality other than faecal occult blood testing is to be considered. Results from trials are essential for sensible public health decisions on cancer screening In this chapter it is shown that they cannot automatically be extrapolated to population screening situations without taking into account epidemiology, demography, screening; quality, policy and history, clinical practice and costs. The role of these components of detailed evaluation of a screening programme are now described in more detail.