Renal tumor growth rate in patients with previously normal CT scan: Analysis of the initial stage of growth.

Objective: Most of the studies regarding natural history of renal masses are based on active surveillance series and suggest that the renal masses have a slow growth rate. Nevertheless, only a few studies report the time between a normal computed tomography (CT) scan to the first detection of a tumor. We aimed to analyze the growth rate in newly diagnosed kidney tumors.

Material And Methods: We analyzed patients with enhancing renal masses that developed after a normal CT scan, which was performed at most 12 months earlier. Variables examined included patient age, gender, tumor size, volume, tumor linear growth rate (LGR). All cases were surgically treated. Mann-Whitney U test was used to compare variables. A p<0.05 was considered as statistically significant.

Results: We found 31 patients with 33 lesions. Male to female ratio was 1.58 (19/12). The average age was 59.2 years (standard deviation [SD]±12.1), and the mean tumor size was 4.27 cm (SD±4.3). Tumor LGR was 0.87 cm/month (range: 0.28-1.66) and presumed to be 10.4 cm at 1 year (range: 3.36-19.9). Tumor LGR for time detection at <6 month or ≥6 months were 1.1 cm/month and 0.68 cm/month (range: 0.27-1.08 and 0.88-1.76, respectively; p=0.0004), respectively. Tumor LGRs for low- and high-grade tumors were 0.89 cm/month and 0.83 cm/month (p=0.65), respectively. Median volume was 36.1 cm (range: 2.61-143.7), and for low and high grade the median volumes were 27.9 cm and 47.6 cm, respectively (p=0.54). Malignant pathology was present in 93.9 % (31 of 33) of masses (lesions).

Conclusion: We found differences in tumor LGR in tumors detected before and after 6 months. We did not find any correlation between tumor growth rate and Fuhrman grade system, gender, histology, or age. We found the highest LGR published up to date.