Prognostic value of the pretreatment CA19-9/Albumin ratio in de novo metastatic colorectal cancer: A retrospective cohort study.

Serum biomarkers that reflect both tumor burden and host response may provide valuable prognostic information in metastatic colorectal cancer (mCRC). Carbohydrate antigen 19-9 (CA19-9) and albumin levels have been associated with disease outcomes; however, the prognostic value of their ratio has not been evaluated in de novo mCRC. This study aimed to investigate the prognostic significance of the pretreatment CA19-9/albumin ratio in patients with de novo mCRC who were treated with standard combination chemotherapy and biologic agents. A total of 178 patients diagnosed with de novo mCRC between 2013 and 2024 were retrospectively analyzed. The CA19-9/albumin ratio was calculated by dividing serum CA19-9 (U/mL) by albumin (g/dL), and the optimal cutoff value was determined using receiver operating characteristic curve analysis. Patients were classified into low- and high-ratio groups. Progression-free survival (PFS) and overall survival (OS) were estimated using the Kaplan-Meier method, and independent prognostic factors were identified through multivariate Cox regression analyses. The optimal cutoff value for the CA19-9/albumin ratio was 5.81. Patients with a high-ratio had significantly shorter PFS (median 9.6 vs 16.1 months, P = .002) and OS (median 23.3 vs 32.6 months, P = .005) compared with those with a low-ratio. In multivariate analyses, a high CA19-9/albumin ratio independently predicted shorter PFS (hazard ratio 0.60, 95% confidence interval [CI] 0.41-0.89, P = .011) and OS (hazard ratio 0.66, 95% confidence interval 0.44-0.99, P = .042). The CA19-9/albumin ratio is a simple, inexpensive, and easily obtainable serum biomarker that independently predicts survival in patients with de novo mCRC. This composite biomarker may better reflect the combined effects of tumor burden and host status, providing additional prognostic value beyond conventional markers. Prospective multicenter studies are warranted for further validation.