Growth Rate Variability Exists Among Renal Cortical Tumors

The objective of a recent study was to assess the volume and maximal diameter of renal neoplasms at serial volumetric CT in order to determine the growth rate distribution of the various sizes and subtypes.

The study has shown that there is a wide range and overlap of growth rates between renal neoplasms of various sizes, subtypes, and grades.

Design
Retrospective analysis.

Participants
Fifty-three patients (34 men, 19 women) who had undergone nephrectomy for renal neoplasm.

Methodology
None of the patients had received preoperative chemotherapy or radiotherapy. Patients had each undergone at least two preoperative contrast-enhanced CT scans that had the same section thickness and were performed at least three months apart. The first and last CT examinations were used for each patient, and two sets of measurements were obtained.

Two investigators reached a consensus regarding maximum tumor diameters and volume without knowledge of tumor type. The greatest diameter was obtained in the axial, perpendicular, and longitudinal planes. The sum of the cross-sectional areas was multiplied by section thickness to calculate tumor volume.

The time interval between the two measurements and the tumor volume at the initial and last CT examination were used to calculate doubling time. The time interval and the maximum cross-sectional diameters were used to calculate growth rate.

Results
There were a total of 53 renal tumors found in 53 study patients. Median age was 70 years for males and 68 years for females. The breakdown of lesion subtypes was as follows: 32 clear-cell renal cell carcinomas, 10 papillary, 6 chromophobe, 4 oncocytoma, and 1 lipid-poor angiomyolipoma.

Maximum tumor diameter ranged from 1 to 12 cm. There were 2 clear-cell renal cell carcinomas, 2 papillary, 1 chromophobe, and 2 oncocytomas that did not increase in volume. Average doubling time was 474 days, and mean growth rate was 5.1 mm/year. Of 53 tumors, 33 measured ?3.5 cm; of these, 17 were clear-cell carcinomas.

There was no difference in doubling time between these small tumors and those measuring >3.5 cm. Clear-cell renal cell carcinomas were found to be the faster-growing subtype, and those with higher grades had higher growth rates. However, there was no correlation found between doubling time and initial volume, subtype, or grade.

Reviewer’s Comments
The results of this study showed that small tumors have a similar growth rate as larger ones of similar subtype. Faster-growing tumors are more likely to be clear-cell renal carcinomas, and those with a higher grade demonstrate a faster growth rate.

One of the limitations reported in this study was that the manual technique was used to acquire the cross-sectional area in order to calculate tumor volumes. More accurate results may be acquired if uniform thin-section thickness and automated volumetric measurements are available.

Author: John C. Sabatino, MD, MSD

Reference:
Zhang J, Kang SK, et al. Distribution of Renal Tumor Growth Rates Determined by Using Serial Volumetric CT Measurements. Radiology; 2009; 250 (January): 137-144: