Introduction:

Cystic renal cell carcinomas (cRCC) are suggested to be clinically indolent. As such, a distinct pathologic staging category for these lesions was recently proposed. These recommendations fail to account for limitations in the ability of modern imaging to differentiate cRCC from the rare 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, laterality, Bosniak classification, histology, grade, size, and nearness to the collecting system were recorded. Associations between tumor grade and patient/tumor characteristics were evaluated using generalized estimating equations.

Results:

Eighty-nine patients (n=102 cystic lesions) met strict inclusion criteria; the majority (77%) were older than 50 years of age with a median Charlson comorbidity index was 1.15 (SD1.48). Of the 102 clinically cystic renal masses, 26% were pathologically confirmed as high grade RCC, while 74% were low grade RCC (n=50) or benign (n=26). 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.

Conclusion:

Proposed changes to the kidney cancer staging system define a tumor’s cystic nature based on pathologic examination, however the decision for surgical intervention is based on preoperative radiographic evaluation. Proceeding with surgery for a radiographically “cystic” renal mass was a rare event in our cohort; however, among those who were selected for surgery, about one fourth harbored high-grade pathology. Before making changes to the clinical RCC staging system, a better understanding of the limitations inherent to radiographic characterization of cystic renal masses is necessary.

Funding: n/a