Prognostic value of the Controlling Nutritional Status (CONUT) score in cancer: an umbrella review of systematic reviews and meta-analyses

Background The Controlling Nutritional Status (CONUT) score, combining serum albumin, total cholesterol, and lymphocyte count, has shown promise as a prognostic biomarker in various cancers, but a comprehensive assessment across different cancer types remains lacking. Methods We systematically searched PubMed, Embase, Web of Science, and the Cochrane Database of Systematic Reviews from inception to October 2025 and identified 40 meta-analyses reporting 86 outcomes [7 non-statistically significant ( P ≥ 0.05) and 79 statistically significant ( P < 0.05)] related to the CONUT score and cancer prognosis. The corrected covered area (CCA) was computed to assess study overlap and evidence independence among pooled meta-analyses. The methodological quality of the included studies was evaluated using the AMSTAR, while the quality of the evidence was assessed using the GRADE. Pooled effect sizes, including hazard ratios (HRs), odds ratios (ORs), and relative risks (RRs), along with their 95% confidence intervals (CIs), were directly extracted. Heterogeneity was assessed using the I 2 statistic and Cochran's Q test, and publication bias was evaluated using Egger's regression test. Results A high CONUT score was suggested to be associated with poor prognosis across multiple cancer types. Among the 79 statistically significant outcomes, pooled HRs ranged from 1.19 to 3.94, RRs from 1.22 to 5.38, and ORs from 1.64 to 4.02. Most included meta-analyses (40%) focused on digestive system tumors. Moderate-quality evidence was identified for 10 outcomes. Notably, a high CONUT score was associated with increased postoperative mortality, with a pooled OR of 4.02 in patients with malignant tumors (MTs) and an RR of 5.38 in those undergoing gastrointestinal and hepatopancreatobiliary (GI-HPB) cancer surgery; both analyses showed no heterogeneity (I 2 = 0%) and moderate-quality evidence. Conclusion The available evidence, predominantly of low or very low quality (76/86 outcomes, 88.4%), suggests elevated CONUT scores are associated with poor prognosis across multiple cancer types. Moderate-quality evidence supports this association in specific contexts—including colorectal cancer, bladder cancer, and postoperative mortality in MTs and GI-HPB surgery—suggesting potential prognostic utility. However, given the overall low quality and substantial heterogeneity, routine clinical use of the CONUT score as an independent decision-making tool is not currently warranted. Systematic review registration https://www.crd.york.ac.uk/PROSPERO/ , identifier: CRD420261340659.