Impact of comorbidity on cancer screening and diagnosis

The presence of coexistent chronic disease or comorbid illness has been shown to have an impact on the pathogenesis of cancer and on the frequency of screening, the stage at diagnosis, the intensity of treatment, and, therefore, on cancer outcomes. This chapter will focus on how comorbid illness affects cancer screening and diagnosis. There is some disagreement in the literature regarding how the comorbidity burden affects the screening and stage of cancer, particularly when specific comorbidities and the overall burden of comorbidity, measured by some aggregate index, are examined. Moreover, the extent of the relationship between comorbidity and cancer may be affected by the method by which the comorbidity burden is measured, with regard to breadth (number of comorbidities) and depth (severity of comorbidities). We consider some of these factors in this chapter as we examine the literature in view of four hypotheses: (1) The surveillance hypothesis, which suggests that patients with comorbid illnesses are screened more regularly or are more likely to be diagnosed earlier because they have more frequent contact with the medical care system. (2) The competing demand hypothesis, which posits that patients with comorbidities are screened less or diagnosed later because other chronic conditions represent a competing demand upon physician time and focus. (3) The physiological hypothesis, which argues that comorbid illness actually affects the pathogenesis, progression, and/or severity of cancer. (4) The death from other causes hypothesis, which suggests that patients or their physicians choose not to screen, because of the risk of death from a cause of other than cancer.