Biomarkers of systemic inflammation provide additional prognostic stratification in cancers of unknown primary

Abstract Background Biomarkers of systemic inflammation have been shown to predict outcomes in patients with cancer of unknown primary (CUP). We sought to validate these findings in patients with confirmed CUP (cCUP) and explore their role alongside existing clinicopathological prognostic categories. Patients and Methods CUP oncologist from across the United Kingdom were invited to include patients with cCUP referred to their local CUP multidisciplinary team. Patient demographics, clinical, pathological and outcome data were recorded and analysed. Results Data were available for 548 patients from four CUP services. 23% ( n = 124) of patients met clinicopathological criteria for favourable‐risk cCUP. On multivariate analysis c‐reactive protein (CRP) ( p < 0.001) and the Scottish Inflammatory Prognostic Score (SIPS: combining albumin and neutrophil count) ( p < 0.001) were independently predictive of survival. CRP and SIPS effectively stratified survival in patients with both favourable‐risk and poor‐risk cCUP based on clinicopathological features. Conclusions Biomarkers of systemic inflammation are reliable prognostic factors in patients with cCUP, regardless of clinicopathological subgroup. We recommend that CRP or SIPS are incorporated into routine clinical assessments of patients with cCUP as a tool to aid investigation and/or treatment decision‐making across all groups. Established clinicopathological factors can then be used to inform management pathways and specific systemic anticancer therapy selection.