Combined plasma C-reactive protein, interleukin 6 and YKL-40 for detection of cancer and prognosis in patients with serious nonspecific symptoms and signs of cancer

Background and methods: Inflammation is a hallmark of cancer and its progression. Plasma levels of C-reactive protein (CRP), interleukin-6 (IL-6) and YKL-40 reflect inflammation, and are elevated in patients with cancer. This study investigated whether plasma CRP, IL-6 and YKL-40 had diagnostic value in 753 patients referred with nonspecific signs and symptoms of cancer to a diagnostic outpatient clinic. Results: In total, 111 patients were diagnosed with cancer within 3 months and 30 after 3 months. CRP, IL-6 and YKL-40 were elevated in 44%, 60% and 45% of the cancer patients, and in 15%, 33% and 25% of the patients without cancer. Elevated levels of all three markers were associated with risk of cancer within 3 months: CRP (odds ratio (OR) 4.41, 95% confidence interval (CI) 2.86–6.81), IL-6 (OR = 2.89, 1.91–4.37) and YKL-40 (OR = 2.42, 1.59–3.66). Multivariate explorative analyses showed that increasing values were associated with the risk of getting a cancer diagnosis (continuous scale: CRP (OR = 1.28, 1.12–1.47), carcinoembryonic antigen (CEA) (OR = 1.61, 1.41–1.98), CA19-9 (OR = 1.15, 1.03–1.29), age (OR = 1.29, 1.02–1.63); dichotomized values: CRP (OR = 2.54, 1.39–4.66), CEA (OR = 4.22, 2.13–8.34), age (OR = 1.42, 1.13–1.80)). CRP had the highest diagnostic value (area under the curve = 0.69). Combined high CRP, IL-6 and YKL-40 was associated with short overall survival (HR = 3.8, 95% CI 2.5–5.9, p < 0.001). Conclusion: In conclusion, plasma CRP, IL-6 and YKL-40 alone or combined cannot be used to identify patients with cancer, but high levels were associated with poor prognosis. CRP may be useful to indicate whether further diagnostic evaluation is needed when patients present with nonspecific signs and symptoms of cancer.