Anaemia of inflammation and cancer risk according to comorbidity in patients aged 40–89 years: a Danish cohort study

Anaemia of inflammation represents a common form of anaemia. It is often clinically linked to pre-existing comorbidities but can also be a sign of cancer. This challenges the diagnostic evaluation, making it difficult to determine whether anaemia of inflammation results from existing comorbidity or indicates an underlying malignancy. However, the cancer risk remains poorly investigated in patients with new-onset anaemia of inflammation in relation to pre-existing comorbidity. Therefore, we aimed to assess the cancer risk in patients with new-onset anaemia of inflammation in a general practice setting according to comorbidity status. This observational population-based cohort study was based on data from laboratory systems in the North- and the Central Denmark Region combined with data in selected national healthcare registers. We included patients aged 40–89 years with new-onset anaemia of inflammation between January 2013 and December 2018. Patients with a prior history of cancer were excluded. The primary outcome measure was the cancer incidence within 12 months of the anaemia index date, stratified by comorbidity. A total of 2,640 patients (median [interquartile interval] age 70 [62–79] years; 61.1% men) were included. In total, 16.9% (95% confidence interval (CI): 15.5–18.3) of patients with new-onset anaemia of inflammation were diagnosed with cancer within 12 months. Notably, patients without pre-existing comorbidities had the highest cancer incidence at 20.8% (CI: 18.7–22.8), while those with pre-existing comorbidity also demonstrated a significant cancer incidence of 11.7% (CI: 9.8–13.5). This represents a cancer incidence proportion ratio of 1.78 (CI:1.48–2.15). In the adjusted Cox regression analysis, the cancer risk was significantly higher in patients without pre-existing comorbidity compared to patients without comorbidity (hazard ratio 1.89, CI:1.54–2.32). This study showed a significant cancer incidence linked with new-onset anaemia of inflammation, particularly in patients without pre-existing comorbidities, which doubled the cancer incidence compared to patients with pre-existing comorbidity. It is crucial to remain aware of the cancer risk when assessing patients with new-onset anaemia of inflammation, especially in those without pre-existing comorbidity, to ensure appropriate detection of potential underlying malignancy in this high-risk population.