Urologic Oncology: Seminars and Original Investigations
Original articleDeclining incidence of benign lesions among small renal masses treated with surgery: Effect of diagnostic tests for characterization
Introduction
With the increased use of cross-sectional imaging modalities, the incidence of localized renal cell carcinoma (RCC) has been increasing during the last 3 decades, with the greatest increase observed in small renal masses (SRMs), usually defined as having a radiological diameter of<4 cm [1], [2], [3]. However, at the same time, the incidence of benign histology in surgical specimens has increased as the size of renal masses has decreased, even in renal masses suspected to be RCC on preoperative diagnostic examinations [4].
In the current clinical guidelines, contrast-enhanced multiphase computed tomography (CT) is considered the most reliable radiologic examination for characterizing renal masses before surgery [5]. However, the characteristics of some renal tumors remained indeterminate even with multiphase CT [6]. Because surgery for benign renal tumors is generally considered nonbeneficial [7], [8], recent imaging studies and renal mass biopsy (RMB) have been widely used to identify histologic characteristics before definitive management; magnetic resonance (MR) imaging has been reported to be an effective method for distinguishing angiomyolipomas (AML) from RCC [9] and percutaneous RMB has shown high diagnostic accuracy for distinguishing benign lesions from RCC with a tolerable rate of complications [2], [10]. Despite imaging or tissue acquisition suggesting a benign result, a fair number of patients still undergo surgery for their SRM [8], [11], [12], [13].
As mentioned earlier, variable imaging studies and RMB have been widely used to identify tumor histology before definitive management, and these efforts may have impacted trends in the incidence of benign lesions after surgery for SRM over time. However, to our knowledge, no studies have been conducted to elucidate this issue because multiple factors (i.e., level of evidence, cost, insurance system in each country, etc.) could affect the use of diagnostic tests for SRMs. We thereby sought to evaluate the changes in the incidence of benign lesions in SRMs by surgery year, which might reflect the change in diagnostic tests used, with a large cohort of patients with SRMs during the past 15 years.
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Patient cohort
A total of 2,707 patients who underwent curative surgery for SRMs (<4 cm) at our institute from January 2001 to December 2015, including 683 patients who underwent radical nephrectomy and 2,024 patients who underwent partial nephrectomy, were included in this study. Diagnostic procedures and surgical methods performed in the 2,707 patients are depicted in the Fig. The electronic medical records of these patients were retrospectively reviewed to retrieve the detailed demographic and clinical
Results
Of 2,707 patients, benign histology was identified in 192 (7.1%) patients. Among 192 patients with benign lesions, oncocytoma was identified in 71 patients (37.0%), AML in 79 patients (41.1%), and other benign lesions in 42 patients (21.9%). Among cases with malignant histology, clear cell RCC was detected in 2,065 patients (82.1%), papillary RCC in 209 patients (8.3%), chromophobe RCC in 169 patients (6.7%), and other malignant lesions in 72 patients (2.9%).
The uses of multiphase CT (84.3%,
Discussion
To avoid unnecessary surgeries for misclassified benign renal masses, clinicians generally make every effort to distinguish benign renal masses from RCC. However, a considerable number of surgeries are still performed for benign renal masses owing to preoperatively misclassified lesions [4], [19], [20]. This problem is believed to be more serious than before because the size of renal masses becomes smaller as the incidence of incidentally detected renal masses has increased over time [21].
Conclusions
Our study showed that in a large cohort of patients receiving curative surgery for SRMs, the incidence of benign histology after surgery for SRMs has declined in recent years. The recent increased use of RMB, in addition to the effect of evolving imaging techniques and implanting MRI, might be associated with the decreased incidence of benign histology. In the future, a large population-based study will be needed to assess the effects of these diagnostic tests on the incidence of benign
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