Small renal masses grow slowly; surveillance is key

Philadelphia-Enhancing renal masses are all presumed to be renal cell carcinoma until proven otherwise. While surgery remains the gold standard, those that are watched instead of excised carry a relatively low risk of metastasis. Unfortunately, size on presentation cannot tell clinicians about their true growth potential. Because not all enhancing renal masses are RCC, those that are, in fact, carcinomas grow faster than the masses left in place. Those are the conclusions of two different studies on the natural history of renal masses, one, a meta-analysis of the world literature and the other, an analysis of one center's experience.

"The practice of observation of these lesions in selected patients-those who are either unfit or unwilling to go to surgery-is not uncommon," said Temple University Hospital resident Paul Crispen, MD, who presented the meta-analysis at the AUA annual meeting in San Antonio.

To be included, the studies had to clearly distinguish metastatic from localized disease. Then the team analyzed the number of lesions followed, the mean lesion size at presentation, the mean lesion growth rate, the duration of follow-up, any available pathologic studies, and the rate of progression to metastatic disease.

However, analysis showed no correlation between size at presentation and the growth rate. On the other hand, a subset analysis showed that the mean growth rate of the lesions pathologically confirmed to be renal cell carcinomas was significantly faster than that of the lesions that were not removed and that were simply observed (0.42 vs. 0.21 cm/year).

Forty-six percent of the lesions in the analysis had pathologic data available for review. Of those, 92% proved to be malignant (the remaining 8% were oncocytomas or other benign neoplasms). Nevertheless, only three lesions, or 1%, progressed to metastatic disease during active surveillance.

RCCs grow faster

Similar experience was reported at the meeting by a team led by Stuart Wolf, MD, who is director of the Michigan Center for Minimally Invasive Urology at the University of Michigan in Ann Arbor. They analyzed data from at least 1 year of follow-up (mean 29 months) of 39 patients with 45 solid renal masses. Twenty-six of these patients chose surveillance because of their advanced age or comorbidities, and the remainder based the decision on preference.

Mean lesion size at presentation was similar to that in the meta-analysis-2.1 cm (range, 0.8 to 5 cm). The mean growth rate, 0.26 cm/year, was nearly identical to that in the meta-analysis. Follow-up continues on 32 of the masses. In those patients, the mean growth rate of the mas-ses is 0.10 cm/year.