Viable tumor volume: Volume of interest within segmented metastatic lesions, a pilot study of proposed computed tomography response criteria for urothelial cancer

• It is clear that 2D axial measurements are incomplete assessments in metastatic disease; especially in light of evolving antiangiogenic therapies that can result in tumor necrosis.
• Our pilot study demonstrates that taking volumetric density into account can better predict overall survival when compared to RECIST, volumetric size, MASS and Choi.
• Although volumetric segmentation and further density analysis may not yet be feasible within routine workflows, the authors believe that technology advances may soon make this possible.

ObjectivesTo evaluate the ability of new computed tomography (CT) response criteria for solid tumors such as urothelial cancer (VTV; viable tumor volume) to predict overall survival (OS) in patients with metastatic bladder cancer treated with cabozantinib.Materials and methodsWe compared the relative capabilities of VTV, RECIST, MASS (morphology, attenuation, size, and structure), and Choi criteria, as well as volume measurements, to predict OS using serial follow-up contrast-enhanced CT exams in patients with metastatic urothelial carcinoma. Kaplan–Meier curves and 2-tailed log-rank tests compared OS based on early RECIST 1.1 response against each of the other criteria. A Cox proportional hazards model assessed response at follow-up exams as a time-varying covariate for OS.ResultsWe assessed 141 lesions in 55CT scans from 17 patients with urothelial metastasis, comparing VTV, RECIST, MASS, and Choi criteria, and volumetric measurements, for response assessment. Median follow-up was 4.5 months, range was 2–14 months. Only the VTV criteria demonstrated a statistical association with OS (p = 0.019; median OS 9.7 vs. 3.5 months).ConclusionThis pilot study suggests that VTV is a promising tool for assessing tumor response and predicting OS, using criteria that incorporate tumor volume and density in patients receiving antiangiogenic therapy for urothelial cancer. Larger studies are warranted to further validate these findings.