Urologic Oncology: Seminars and Original Investigations
Original articleThe metastatic potential of renal tumors: Influence of histologic subtypes on definition of small renal masses, risk stratification, and future active surveillance protocols
Introduction
The increased utilization of cross-sectional imaging has increased the incidence of renal cell carcinoma (RCC) throughout the past 30 years. It has been estimated for 2016 that approximately 62,700 new patients would be diagnosed with RCC, more than 60% incidentally, and approximately 14,240 patients would die of RCC [1]. Despite the fact that significant numbers of patients present with advanced or metastatic RCC (mRCC), most are diagnosed with localized renal tumors, with smaller tumors often referred to as small renal masses (SRMs). Although the traditional AJCC staging system uses tumor size to stratify the risk of Cancer-Specific Survival (CSS), prior studies have shown differences in CSS based on histology after surgical treatment [2], [3], [4].
With increased utilization of active surveillance (AS) and increased awareness of competing mortality risks, the definition of SRM may need to be reconsidered. Should a SRM be based on size alone, such as 3 or 4 or 5 cm? Or is a SRM a tumor that carries a certain metastatic potential? Contemporary management strategy is still largely based on patient preference, comorbidities, tumor size, location, and growth kinetics. The influence of histology in metastatic potential is often overlooked when discussing management options, with size or growth rate often serving as the only triggers for intervention.
In this study, we evaluate the metastatic potential for renal masses based on histology, and hypothesize that the histology of small masses influences the rate of metastatic spread, thus refining the definition of the SRM based on potential for development of metastatic disease progression rather than the size alone.
Section snippets
Materials and methods
Surveillance Epidemiology and End Results (SEER)-18 registries database was queried for all patients≥20 years of age diagnosed with RCC between 2004 and 2012. Several non–clear cell RCC subtypes were added to the International Classification of Diseases for Oncology (ICD-O) code set in 2000 and used starting in 2001 and an updated coding schema was implemented starting in 2004. There were 115,347 renal tumors during this time frame. To minimize rare and mixed histologies, we included only clear
Results
A total of 55,478 cases met our inclusion criteria and included 43,683, 8,587, and 3,208 cases of clear cell, papillary, and chromophobe RCC, respectively. A total of 54,191 (97.7%) were surgically treated. The mean patient age was 61.2 years (range: 20–108) and 63.7% of patients were male. Mean and median tumor size was 5.2 and 4.2 cm, respectively. Table 1 describes patient demographics and tumor characteristics.
Among those with known histology, there were 4,369 (7.9%) who presented with
Discussion
Present SEER analysis demonstrates that the metastatic potential is not only dependent on tumor size but also on histologic subtype. Among the most common histologies, we have demonstrated that with increasing tumor size, clear cell is the most aggressive histology, whereas chromophobe is the least aggressive. It was not surprising that those RCCs characterized as NOS had the highest metastatic rate as these typically include rare but aggressive subtypes, such as sarcomatoid, medullary, or
Conclusions
The metastatic rate of RCC is dependent on the histologic variant of the tumor. The definition of a SRM can potentially be modified to include the metastatic potential and not on the tumor size alone. The histology in addition to the tumor size provides specific risks for development of metastatic disease. This information may be useful for counseling patients regarding management for renal tumors and helpful in expanding and modifying AS protocols.
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