How renal mass biopsy impacts management

At the 2015 Society of Urologic Oncology annual meeting in Washington, J. Stuart Wolf, Jr., MD, addressed concerns about the diagnostic inaccuracies of core renal biopsy in the diagnosis of small renal masses.

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In his presentation, Dr. Wolf argued, “Biopsy does not need to perfectly identify histologic type and grade when it is paired with a risk-stratified, sized-based management algorithm.”

In a study conducted at the University of Michigan, Ann Arbor, where Dr. Wolf is professor of urology, investigators considered an approach that combined core biopsy risk stratification with an algorithm based on size (J Urol 2013; 189:441-6). To test reliability of the approach, the authors compared the treatment assignment (surveillance vs. excision) in 151 patients based on size and biopsy histology with the appropriateness of that assignment as determined by final pathology after surgical excision. Dr. Wolf demonstrated that use of renal mass biopsy, combined with a size-based management algorithm, has an excellent positive predictive value (100% in that study) but an imperfect negative predictive value (86%).

The combination of renal mass biopsy with a size-based management algorithm was also applied to a multi-institutional database compiled by active robotic partial nephrectomy surgeons (J Urol 2014; 192:1337-42). In that study, the authors concluded that about half the patients theoretically could have avoided surgery had the algorithm, which incorporates both size and biopsy histology, been applied preoperatively.

“The greatest liability [of incorporation of renal mass biopsy in treatment decisions] is false negatives,” Dr. Wolf conceded. He noted that, in his updated series, 17% of patients would have been incorrectly assigned to surveillance, and in fact harbored worse pathology than suggested by biopsy. He was reassured, however, that those patients who underwent delayed intervention had similar rates of partial nephrectomy and adverse pathology when compared with those patients who underwent early intervention.

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Furthermore, in patients undergoing surveillance, increasing growth rate was associated with adverse pathology. In data from the University of Michigan, there was a 10% increase in odds of adverse pathology for each 1 mm/year change in growth rate.

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Based on these findings, Dr. Wolf concluded that patients incorrectly assigned to surveillance can be adequately salvaged, mitigating much of the concern about false negative renal biopsy.

Renal mass biopsy also informed type of treatment in those patients who were ultimately treated, said Dr. Wolf. Using a subset of the University of Michigan small renal mass database, he demonstrated that worse pathology on biopsy was associated with increased rate of radical nephrectomy in patients aged 55-75 years.

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Referring to this and other work, Dr. Wolf concluded, “The clinical utility of biopsy is greatest in patients 55 to 75 years of age with tumors 2-4 cm in size.”

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Lastly, Dr. Wolf made a case that renal mass biopsy has not been useful to identify those patients who are likely to be maintained on active surveillance. He pointed to data from his institution that demonstrated that size and growth rate, but not biopsy pathology, was associated with delayed intervention in those patients on surveillance.

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Dr. Wolf left the audience with an air of optimism about the future of renal mass biopsy. He previewed yet-to-be presented data introducing a multi-gene signature with a highly discriminative association with renal cancer recurrence and cancer specific mortality. “We may finally be at the doorstep of the holy grail of renal mass biopsy, which is to get molecular markers to really help us determine the risk for [an individual] patient,” he said.

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