Association between Tumor Size at the Time of Disease Progression and Survival Outcomes

Abstract

Purpose This study evaluates the prognostic significance of tumor size at disease progression (PD) and depth of response (DOR) in cancer patients. Materials and Methods We performed post hoc analysis using data from six prospective clinical trials conducted by the Korean Cancer Study Group. Patients with tumor size at PD was categorized into ‘Mild PD’ and ‘Significant PD’ based on the cutoff values of relative change from baseline using maximally selected rank statistics. The overall survival (OS) and progression-free survival (PFS) were compared between PD and DOR categories. Results Among the 194 evaluable patients, 130 experienced PD. A 35.48% decrease from baseline in tumor size at PD was chosen for the cutoff between mild and significant PD for OS (mild PD: tumor size from the baseline ≤ −35.48%; significant PD > −35.48%). The mild PD had superior OS compared to the significant PD (25.8 vs. 12.8 months; hazard ratio [HR], 0.47; 95% confidence interval [CI], 0.266 to 0.843; p=0.009). When using an exploratory cutoff based on whether the tumor size was below vs. exceeded from the baseline (mild PD: tumor size from the baseline ≤ 0%; significant PD > 0%), OS remained significantly longer in the mild PD (17.1 vs. 11.8 months; HR, 0.60; 95% CI, 0.392 to 0.932; p=0.021). The greatest DOR was associated with the longest OS and PFS (p < 0.001 for both). Conclusion Tumor size at PD and DOR were significant prognostic factors for progressive disease. Maintaining a sufficiently reduced tumor size even during PD was associated with better survival outcomes.