Biomarkers of inflammation are associated with colorectal cancer risk in women but are not suitable as early detection markers

Initial studies have investigated the association between inflammation and colorectal cancer (CRC) using C‐reactive protein (CRP) as a proinflammatory biomarker and have noted inconsistent results among women. We here report the findings from a large prospective study with repeat measurements of CRP, as well as serum amyloid A (SAA), an additional biomarker of inflammation, and risk of CRC. In the Women's Health Initiative Observational Study, we examined associations of CRP and SAA with CRC using repeat assessments (baseline and 3‐year follow‐up) among 953 matched case–control pairs for CRP and 966 pairs for SAA. Multivariate‐adjusted conditional‐logistic regression models were used with two‐sided tests of significance. Receiver operating characteristic (ROC) curve analysis assessed their utility as early detection markers. Colon cancer risk (odds ratio OR] and 95% confidence intervals) among women in the highest quintiles of CRP or SAA compared to those in the lowest quintiles was OR_colon/CRP = 1.37 (0.95–1.97, p‐trend = 0.04) and OR_colon/SAA = 1.26 (0.88–1.80, p‐trend = 0.10), respectively. Women with elevated concentrations of both CRP and SAA had an increased risk of OR_colon = 1.50 (1.12–2.00, p‐value = 0.006) compared to those with low concentrations. No positive associations were observed with rectal cancer and weaker associations for CRC overall. Temporal changes in biomarkers more than 3 years did not predict risk. The area under the 6‐month ROC curve for CRP+SAA was 0.62 (95% confidence interval = 0.55–0.68). Elevated inflammatory biomarkers are associated with an increased risk of CRC, mainly colon cancer. Nevertheless, changes in the biomarkers over time do not suggest that they merit consideration as early detection markers for CRC.