Incidentally detected small renal masses (SRMs) are not always cancer, and even those that are biopsy-proven renal cell carcinoma tend to grow slowly initially and have a low risk of metastasis, according to analyses of data.
"There has been a trend to a stage migration in patients diagnosed with RCC so that incidentally detected SRMs now constitute more than half of new kidney cancers in developed countries," lead author Michael A. Jewett, MD, said at the AUA annual meeting. "We and others have consistently reported that these lesions tend to grow very slowly, but these studies have various limitations, and their findings may lead us to be complacent while underestimating the real risk.
"Longer prospective follow-up is planned, but the early results of our trial indicate active surveillance with delayed treatment for progression is a reasonable initial management option for most patients with asymptomatic SRMs."
Between August 2004 and December 2008, 151 patients with 172 incidentally detected, asymptomatic SRMs that met criteria for T1a RCC were enrolled at eight Canadian centers. Patients were eligible for enrollment if they were elderly, had significant comorbidity, or refused treatment for their kidney tumor. To reduce potential sources of bias, the study excluded patients who were found to have a previously undetected kidney cancer after presenting with metastatic disease, those with less than 2 years of life expectancy or a mass known to have been present for more than 12 months, and those receiving concurrent treatment for other malignancies or with a hereditary renal cancer syndrome.
Seventy-eight patients (52%) underwent recommended percutaneous needle core biopsy. The rate of successful biopsy (ie, retrieval of adequate tissue for a confident diagnosis) was 73%.
Serially, renal imaging was performed at established intervals, depending on biopsy findings and evidence of progression.
During a mean follow-up of 19.3 months (maximum, 48 months), 22 patients were withdrawn from the study by patient or physician preference and eight were lost to follow-up.
Many SRMs are benign
Considering all SRMs, mean tumor diameter at diagnosis was 2.2 cm and the average annual growth rate was only 0.68 mm. A total of 21 tumors in 18 patients showed evidence of progression, defined as local growth to >4 cm, tumor size doubling time <12 months, or metastasis. Sixteen tumors grew locally, only five underwent treatment, and only two patients developed metastatic disease.
"Based on previously available data, we expected a metastatic progression rate up to 5%, but that appears to be a marked overestimate, albeit with the limitation of having relatively short follow-up," Dr. Jewett said.
"However, considering our population of patients is representative of those who would be considered for active surveillance and that they are likely to be dying of other causes, regardless of how many patients are studied, they are not destined to be followed for a long time."
Only 60% of successfully biopsied tumors revealed malignancy. The growth rate for these SRMs that were proven RCC was not significantly different from those that were benign or had no histologic diagnosis.
"Our biopsy findings contain another important message, and that is that a high proportion of these SRMs are benign," Dr. Jewett said.
"This supports the recommendation that we and others have made for performing renal biopsy before any patient undergoes treatment for an SRM suspected to be an RCC."