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Active surveillance of small renal masses appears to be safe, but if intervention does become necessary, what should trigger it?

"We now know that with at least that active surveillance is safe and non-inferior to primary intervention," said Phillip Pierorazio, MD, of the University of Pennsylvania in Philadelphia, during a presentation on the topic at the Society of Urologic Oncology annual meeting. "We know that growth rates are similar and slow -- with very low rates of metastatic progression -- and that delayed intervention is safe."

However, Pierorazio pointed out that nonoperative management of these small masses is still underutilized, with at most 30% of eligible patients getting surveillance. "It shouldn't be 100%, but we can certainly do better."

According to guidelines on active surveillance of small renal masses, clinicians may elect active surveillance for initial management, with the potential for delayed intervention, for patients with a solid renal mass smaller than 2 cm, or those that are complex but predominantly cystic.

Additionally, the guidelines recommend that for patients with a solid or Bosniak 3/4 complex cystic renal mass, "clinicians should prioritize active surveillance/expectant management when the anticipated risk of intervention or competing risks of death outweigh the potential oncologic benefits of active treatment."

Yet Pierorazio noted that an analysis of surgeon-level data showed that just 61.3% offered active surveillance to patients with small renal masses.

"Interestingly, the things we think should drive active surveillance selection -- age, life expectancy, tumor size -- actually don't," he said. "The number one predictor of choice of management treatment is the first urologist [a patient] meets with, and what their practice pattern is."

He referred to studies showing that individual physicians and practices that were more likely to offer prostate cancer active surveillance were also more likely to offer small renal mass active surveillance (and vice versa), and that institutions that do more thyroid surveillance are also more likely to do small renal mass surveillance.

"So there are internal and extrinsic biases and pressures that certainly influence how they offer those things," Pierorazio observed.

And those preferences carry weight with patients, he noted. A recent study in found a physician's recommendation to be the most influential factor for patients' perceptions of active surveillance.

"They really do rely on us," he said. "So to be good stewards of active surveillance and avoid overtreatment of small renal masses, we have to understand what the triggers and time for intervention are."

According to Pierorazio, tumor size is the most reliable predictor of metastatic potential and the best trigger for intervention.

"We know 80% to 90% of masses under 4 cm are either benign or low-grade organ-confined renal cell carcinomas that no one is ever going to die of," he said, adding that the rates of metastatic disease are "incredibly low," at less than 2% for 4 cm tumors and under 1% for tumors smaller than 3 cm.

Another important trigger is the growth rate of the mass, with zero growth suggesting no risk for metastatic disease. "Clear cell renal cell carcinoma is more likely to grow quickly, but not always," he said. "Elevated growth predicts intervention, but importantly doesn't predict metastatic potential."

A big caveat is most of these renal masses are resected before reaching 4 cm, he said. It's not clear what will happen "when we start crossing that threshold, but under 4 cm we are incredibly safe."

Pierorazio added that biopsy can help predict growth rate, but more importantly "helps us avoid overtreatment of benign renal tumors."

Finally, patient preference is "hugely important," he said, pointing out that studies show that patients on active surveillance have greater illness uncertainty and higher distress, which is probably associated with a worse general quality of life because these patients were older and sicker.

However, research has also shown that mental health improves over time in a structured active surveillance program.

And patient preference is a strong indicator for crossover from active surveillance to delayed intervention. Since 2009, about 40% of surveillance patients who crossed over in the Delayed Intervention and Surveillance for Small Renal Masses () registry were "elective crossovers," said Pierorazio.

"Not because their tumor is growing, and not because it got bigger," he said. "But because they wanted to."

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