WCE 2018: Small Renal Masses

Paris, France (UroToday.com) It has been shown that 15-20% of all renal tumors <4 cm (cT1a) are in fact benign and do not need to be treated. This number of benign tumors is even higher in patients with tumors <2 cm. Nevertheless, only 7% of urologists refer patients with renal lesions <4 cm for renal biopsy prior to surgery. That is in contrast to 100% preoperative biopsy rate in other solid malignancies (prostate, liver, breast, pancreas, thyroid). There are several reasons for this poor rate of renal mass biopsy among urologists. One is the belief that a biopsy would not change management. Other possible reasons include a non-diagnostic biopsy, false negative result, complications, fear of tumor seeding, and the fact that the majority of renal biopsies are done by radiologists and not by urologists. Given there are no imaging tests nor biomarkers accurate enough for the detection of renal cancer, renal biopsy is key to the management of small renal masses.

Dr. Obek presented to an audience of urologists that a renal mass biopsy is clearly underutilized. Renal mass biopsy is often an office procedure with no need for hospitalization. It has a relatively short learning curve (a few dozen cases) and can be safely performed by a urologist rather than a radiologist in most cases. The biopsy is ultrasound-guided and thus obviates the need for CT scanners at a hospital setting. Since renal tumors are highly heterogeneous, it is recommended to sample at least 2 cores using an 18-gauge needle. Core needle biopsy is considered superior to aspiration.

Renal mass biopsy is a safe procedure with an acceptably low rate of mainly minor complications. The most common complication is a subcapsular or perirenal hematoma. It is largely subclinical, does not require treatment, and the need for blood transfusion or angioembolization is rare. Hematuria can appear in 5% of patients but it is self-limiting and does not require intervention. Other complications such as pneumothorax or infection are rare. Tumor seeding is exceedingly rare, and only a few case reports are found in the literature.

Ten to 20% of renal mass biopsies are nondiagnostic. This is mostly true for small, endophytic, and cystic lesions. With continuous improvements in imaging and biopsy techniques, the actual rate of nondiagnostic biopsies is around 10%. A repeat biopsy, however, is diagnostic in 80-100% of cases. Sensitivity and specificity of renal mass biopsy are both 96-99%, and are noninferior, if not superior to biopsies of other solid organ tumors. The diagnostic accuracy for tumor grade using the 4-grade system is 63%. However, when using low (grade 1-2) or high (grade 3-4) grading system, accuracy increases to 88%.

In conclusion, renal mass biopsy is an office procedure that can often be performed by a urologist using ultrasound guidance. It is a safe procedure with lower complications rate. The diagnostic accuracy is comparable to biopsies of other solid organs. Biopsy of small renal masses, however, remains underutilized among urologists.

Presented by: Can Obek, MD, Professor, Department of Urology, Acibadem Taksim Hospital, Istanbul, Turkey

Written by: Shlomi Tapiero, MD, Department of Urology, University of California-Irvine, medical writer for UroToday.com at the 36th World Congress of Endourology (WCE) and SWL - September 20-23, 2018 Paris, France

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