Monocyte number associated with incident cancer and mortality in middle-aged and elderly community-dwelling Danes

Background: Monocytes play an important role in innate immunity and exhibit prognostic value in some cancers. It was hypothesised that activation of the innate immune system through mobilisation of monocytes to tissue macrophages develops an inflammatory state associated with increased risk of cancer and mortality.

Methods: To test this hypothesis monocyte number was measured in a sample of 669 Danish men (59%) and women (41%) aged 55 to 75 years who were free of any known prevalent cancer or cardiovascular disease. The population was followed for 6.3 years, during which period incident cancers and deaths were compiled from validated national registries.

Results: Fifty-two subjects developed cancer and 83 subjects died during follow-up. The upper quintile of monocyte number (median 0.44×10⁹/L, lower quintile <0.33, upper quintile >0.60) was associated with an increased risk of cancer (hazard ratio [HR] 2.00 [95% CI 1.12-3.57]) and deaths (HR 1.67 [1.03-2.72]) in univariate analyses, after correction for age and gender (cancer HR 2.15 [1.20-3.86] and death HR 1.63 [1.00-2.67]), and following additional correction for smoking habits, diabetes, systolic blood pressure, and total cholesterol (cancer HR 2.00 [1.10-3.70] and death HR 1.30 [0.78-2.16]). COX regression models, with inclusion of the aforementioned explanatory variables and added heart rate variability, alcohol use, and CRP, revealed monocyte count (per 0.1×10⁹/L increase) to be independently associated with incident cancer (HR 1.12 (1.05-1.19)) and death (HR 1.13 (1.06-1.19)).

Conclusions: In healthy middle-aged and elderly community-dwelling Danes circulating monocytes independently predicted incident cancer and mortality.