Introduction

Cystic renal cell carcinomas (RCC) are suggested to be clinically indolent. As such, a distinct pathologic staging category for these lesions was recently proposed. While not without merit, these recommendations fail to account for limitations in the ability of modern imaging to differentiate cystic RCC from more biologically aggressive mimics. We evaluated the frequency of high grade kidney cancer in the highly selected cohort of surgically resected renal masses having cystic appearance on pre-operative radiographic imaging.

Methods

A prospectively maintained institutional database was queried for clinically cystic renal masses that underwent surgery from January 2000 - June 2016 (n=2,729 kidney surgeries). Patient and tumor characteristics including age at surgery, smoking history, Charlson comorbidity index (CCI), gender, race, BMI, surgery date, laterality, Bosniak classification, histology, grade, size, and nearness to the collecting system were tabulated. Associations between tumor grade and patient/tumor characteristics were evaluated using generalized estimating equations.

Results

Eighty-nine patients (n=101 cystic lesions) met strict inclusion criteria; the majority (77%) were older than 50 years of age and the mean Charlson comorbidity index was 1.15 (SD1.48) (Table 1). Of the 101 clinically cystic renal masses, 23% were confirmed pathologically as high grade RCC while 77% were low grade RCC (n=56) or benign (n=22). CCI was associated with high grade surgical pathology (OR 1.37, 95% CI 1.05-1.79, p = 0.02). There was no association between tumor grade and the remainder of the patient/tumor characteristics analyzed.

Conclusions

Recently proposed changes to the kidney cancer staging system define a tumor's cystic nature based on pathologic examination. Proceeding with surgery for a radiographically "cystic" renal mass was a rare event in our cohort; however, among those that went onto surgery, nearly a quarter harbored high grade pathology. Before making changes to the clinical RCC staging system, a better understanding of the limitations inherent to radiographic determination of low malignant potential, cystic renal masses is necessary.

Funding

None