The systemic immune‐inflammation index is associated with an increased risk of incident cancer—A population‐based cohort study

Several studies found that the systemic immune‐inflammation index (SII) is a prognostic factor for mortality in patients with solid tumors. It is unknown whether an increased SII in generally healthy individuals reflects a risk for developing cancer. Our objective was to investigate the association between the SII and incident cancers in a prospective cohort study. Data were obtained from the Rotterdam Study; a population‐based study of individuals aged ≥45 years, between 2002 and 2013. The SII at baseline was calculated from absolute blood counts. The association between the SII and the risk of any solid incident cancer during follow‐up was assessed using Cox proportional hazard models. Individuals with a prior cancer diagnosis were excluded. Data of 8,024 individuals were included in the analyses. The mean age at baseline was 65.6 years (SD 10.5 years) and the majority were women. During a maximum follow‐up period of 10.7 years, 733 individuals were diagnosed with cancer. A higher SII at baseline was associated with a 30% higher risk of developing a solid cancer (HR of 1.30 [95% CI; 1.11–1.53]), after adjustment for age, sex, socioeconomic status, smoking, BMI and type 2 diabetes. The absolute cumulative 10‐year cancer risk increased from 9.7% in the lowest quartile of SII to 14.7% in the highest quartile (p‐value = 0.009). The risk of developing cancer was persistent over time and increased for individuals with the longest follow‐up. In conclusion, a high SII is a strong and independent risk indicator for developing a solid cancer.