Tumor Doubling Time of Renal Cell Carcinoma Measured by CT: Collaboration of Japanese Society of Renal Cancer

Objective: This study was conducted to examine the natural history of renal cell carcinoma (RCC). Methods: Inclusion criteria were the following: (1) patients who received diagnostic imaging of the kidney (CT, MRI) at two points in time before the diagnosis of RCC or patients who were followed, without treatment, after a diagnosis of RCC; and (2) patients in whom changes in tumor size were followed by the same modality of diagnostic imaging and who did not receive any treatment which could exert anti-tumor activity on the primary or metastatic lesions. The tumor doubling time (DT) and the growth rate of maximum tumor diameter (R) were determined. DT was calculated using the equation DT = (T – T0) × log2/logV – logV0 (where T – T0 indicates the length of time between two measurements and V0 and V denote the tumor volume at two points of measurement). R was calculated using the equation R = (ϕ – f0)/(T – T0) × 100 (where ϕ0 and f indicate the maximum diameter at two points). Fifty-six cases registered with the Japanese Society of Renal Cancer were included in the evaluation. Results: DT was 603.1 ± 510.1 days, which did not correlate with V0. R was 0.263 ± 0.346 cm/day × 100. In cases where the tumor diameter was ≥4 cm, a significant correlation was noted between f0 and R. Conclusions: Elucidation of the natural history of RCC will contribute to facilitation of differential diagnosis and determination of optimum therapeutic strategy.