What is comorbidity?

Abstract

Comorbidity is “any distinct additional clinical entity that has existed or that may occur during the clinical course of a patient that has the index disease under study”. It is related to, but distinct from other constructs such as multimorbidity, functional status, disability, allostatic load, frailty, burden of disease and patient complexity. As populations age, the prevalence of chronic disease increases. As a consequence, many people live with, rather than die from chronic health conditions. Cancer is often a chronic disease itself, and is also more prevalent among the elderly. This confluence in timing means that many cancer patients (if not most) live with at least one other chronic disease, although the prevalence of comorbidity varies markedly across populations with different types of cancer. There are several reasons why cancer and comorbidity co-exist, cancer and other long-term conditions share common risk factors, some chronic conditions or their treatments are causally related to cancer and there may be some instances where there are common physiological pathways between cancer and other conditions.