Multimorbidity and cancer outcomes: a need for more research

Cancer incidence increases with age, and about 43% of men and 30% of women aged 65 will develop cancer in their remaining lifetimes.1 The global population is rapidly aging, and by 2030 about 70% of cancer in, for example, the US, will be diagnosed in older patients.2 Fortunately, cancer survival has improved and 5-year survival exceeds 80% for many common cancers.3 As a result of these two complementary trends, the population of cancer survivors is growing at a rate of almost 2% per year.4 As comorbidities accumulate with age, the number of patients with multimorbidity, ie, the coexistence of several chronic diseases, is increasing dramatically.5 In the US, about 80% of Medicare funds are spent on patients with four or more chronic conditions. Multimorbidity is associated with mortality, disability, low functional status, and risks of adverse drug events.6,7 Clinical and epidemiological research on cancer prognosis has mainly focused on cancers in isolation, ignoring the impact of comorbidity and co-medication on the risk of complications and mortality. Comorbidity is a medical condition that exists at the time of diagnosis of the cancer or later, but which is not a consequence of the cancer itself.8 Comorbidity is common in cancer patients, who often have adverse lifestyle factors such as alcohol use, obesity, and smoking, which cause other chronic diseases. Thus, many cancer patients have chronic disorders such as chronic obstructive pulmonary disease, acute myocardial infarction, stroke, metabolic syndrome, and osteoporosis.9–13 With the growing population of elderly patients with cancer and other chronic diseases, modern medicine will need to address multiple medical problems at once, focusing on mortality, treatment complications, quality of life, and implications for screening.7,14 In this issue of Clinical Epidemiology, comprehensive data on the impact of comorbidity and survival in cancer patients are reported. These provide very important insight into the association between multimorbidity and cancer prognoses. These analyses underscore the need for comprehensive, well-designed observational research on comorbidity and cancer. Findings from such types of research can be translated into clinical practice through development, testing, and implementation of intervention strategies designed to minimize the impact of comorbidity and the complications of cancer and its treatment. Such research is urgently needed since many cancer patients with multimorbidity have not benefitted from the recent advances in cancer treatment.