Tumor Volume Evaluation is a Superior Predictor of Prognosis Compared to RECIST in Metastatic Pancreatic Ductal Adenocarcinoma Undergoing Immunochemotherapy

Objective To compare tumor diameter and volumetric assessment for evaluating treatment response and predicting overall survival (OS) in metastatic pancreatic ductal adenocarcinoma (mPDAC) patients treated with immunochemotherapy. Methods This retrospective study included patients with mPDAC treated with immunochemotherapy (June 2021 - May 2024) who underwent pre- and post-treatment contrast-enhanced CT scans. Tumor response was evaluated by measuring the change of diameter, volume, and CA19-9 at 8-week follow-up. Patients were categorized into partial response (PR), stable disease (SD), and progressive disease (PD) groups using diameter and volume, respectively. OS was compared using Kaplan–Meier curves analysis with log-rank tests. Independent predictors of OS were identified via Cox regression and incorporated into a nomogram. Results Among 89 patients (59 ± 8.8 years; 67 male), median OS was 327 days. Tumor evaluation using volumetric category (VOT) provided superior OS stratification between PR and SD compared to RECIST 1.1 ( p = .04 vs. p = .29). Multivariate Cox regression identified VOT as an independent predictor of poor OS (HR, 2.51; 95% CI: 1.32, 5.00; p = .007), and BMI for better OS (HR, 0.89; CI: 0.80, 0.99; p = .04). The nomogram performed well in predicting 1-year and 2-year survival, with area under the ROC curve (AUC) of 0.70 (CI: 0.59 – 0.82) and 0.80 (CI: 0.68 – 0.93), respectively. Conclusion Volumetric CT assessment enables more accurate early survival stratification in mPDAC patients receiving immunochemotherapy than RECIST 1.1.