Preoperatively Misclassified, Surgically Removed Benign Renal Masses: A Systematic Review of Surgical Series and United States Population Level Burden Estimate

Purpose: A significant proportion of renal masses removed for suspected malignancy are histologically benign with the probability inversely proportional to lesion size. To our knowledge the number of preoperatively misclassified benign renal masses treated with nephrectomy is currently unknown. Given the increasing incidence and decreasing average size of renal cell carcinoma, this burden is likely increasing. We estimated the population level burden of surgically removed, preoperatively misclassified benign renal masses in the United States. Materials and Methods: We systematically reviewed the literature for studies of pathological findings of renal masses removed for suspected renal cell carcinoma based on preoperative imaging through July 1, 2014. We excluded studies that did not describe benign pathology and with masses not stratified by size, and in which pathology results were based on biopsy. SEER data were queried for the incidence of surgically removed renal cell carcinomas in 2000 to 2009. Results: A total of 19 studies of tumor pathology based on size met criteria for review. Pooled estimates of the proportion of benign histology in our primary analysis (American studies only and 1 cm increments) were 40.4%, 20.9%, 19.6%, 17.2%, 9.2% and 6.4% for tumors less than 1, 1 to less than 2, 2 to less than 3, 3 to less than 4, 4 to 7 and greater than 7, respectively. The estimated number of surgically resected benign renal masses in the United States from 2000 to 2009 increased by 82% from 3,098 to 5,624. Conclusions: These estimates suggest that the population level burden of preoperatively misclassified benign renal masses is substantial and increasing rapidly, paralleling increases in surgically resected small renal cell carcinoma. This study illustrates an important and to our knowledge previously unstudied dimension of overtreatment that is not directly quantified in contemporary surveillance data.