Cancer risk in persons with new-onset anaemia: a population-based cohort study in Denmark

Background: The time interval from first symptom and sign until a cancer diagnosis significantly affects the prognosis. Therefore, recognising and acting on signs of cancer, such as anaemia, is essential. Evidence is sparse on the overall risk of cancer and the risk of specific cancer types in persons with new-onset anaemia detected in an unselected general practice population. We aimed to assess the risk of cancer in persons with new-onset anaemia detected in general practice, both overall and for selected cancer types. Methods: This observational population-based cohort study used individually linked electronic data from laboratory information systems and nationwide healthcare registries in Denmark. We included persons aged 40–90 years without a prior history of cancer and with new-onset anaemia (no anaemia during the previous 15 months) detected in general practice in 2014–2018. We measured the incidence proportion and standardised incidence ratios of a new cancer diagnosis (all cancers except for non-melanoma skin cancers) during 12 months follow-up. Results: A total of 48,925 persons (median [interquartile interval] age, 69 [55–78] years; 55.5% men) were included in the study. In total, 7.9% (95% confidence interval (CI): 7.6 to 8.2) of men and 5.2% (CI: 4.9 to 5.5) of women were diagnosed with cancer during 12 months. Across selected anaemia types, the highest cancer incidence proportion was seen in women with ‘anaemia of inflammation’ (15.3%, CI: 13.1 to 17.5) (ferritin > 100 ng/mL and increased C-reactive protein (CRP)) and in men with ‘combined inflammatory iron deficiency anaemia’ (19.3%, CI: 14.5 to 24.1) (ferritin < 100 ng/mL and increased CRP). For these two anaemia types, the cancer incidence across cancer types was 10- to 30-fold higher compared to the general population. Conclusions: Persons with new-onset anaemia detected in general practice have a high cancer risk; and markedly high for ‘combined inflammatory iron deficiency anaemia’ and ‘anaemia of inflammation’. Anaemia is a sign of cancer that calls for increased awareness and action. There is a need for research on how to improve the initial pathway for new-onset anaemia in general practice.