BACKGROUND: Multimorbidity is a growing challenge worldwide. In this nationwide study, we investigated the prevalence of multimorbidity and polypharmacy at the time of diagnosis across 20 cancers.

METHODS: We conducted a nationwide register-based cohort study of all Danish residents with a first primary cancer diagnosed between 1 January 2005 and 31 December 2015. Multimorbidity was defined as one or more of 20 conditions (131 specific diagnoses) registered in the Danish National Patient Registry < 5 years before the cancer diagnosis. Polypharmacy was defined as five or more medications registered in the Danish National Prescription Registry and redeemed twice 2-12 months before the cancer diagnosis.

RESULTS: We included 261,745 patients with a first primary cancer, of whom 55% had at least one comorbid condition at diagnosis and 27% had two or more. The most prevalent conditions at the time of cancer diagnosis were cardiovascular disease, chronic obstructive pulmonary disease, diabetes, stroke and depression/anxiety disorder. Polypharmacy was present in one-third of the cancer patients with antihypertensives, anti-thrombotic agents, anti-hyperlipidaemic agents, analgesics and diuretics as the most prevalent redeemed medications.

CONCLUSION: Among patients with a newly established cancer diagnosis, 55% had at least one comorbid condition and 32% were exposed to polypharmacy.