To investigate the prevalence and predictors associated with benign lesions in Korean patients after partial nephrectomy for presumed renal cell carcinoma (RCC) for lesions measuring ≤ 4 cm.

We retrospectively investigated the medical records of 376 patients who underwent partial nephrectomy for presumed RCC with renal masses of size ≤ 4 cm between June 1997 and December 2008. Demographic and clinicopathologic parameters were compared between benign lesions and RCC. Logistic regression was done to identify parameters associated with benign lesions.

In the 376 patients, 81 tumors (21.5%) were benign, including 35 angiomyolipomas (9.3%), 26 complicated cysts (6.9%), 11 oncocytomas (2.9%), and 9 others (2.4%). Univariate analysis showed that time of surgery, female sex, younger age, and normal body mass index (body mass index (BMI) < 23 kg/m²) were associated with benign pathologic findings. On multiple logistic regression analysis, female sex (OR, 4.91; 95% CI, 2.76-08.75; P < .001), age (OR, 0.97; 95% CI, 0.95-0.99; P = .009), and time of surgery (OR, 0.33; 95% CI, 0.11-0.95; P = .040) were independent predictors of benign histologic features. Tumor size, incidental diagnosis, and BMI were not significant predictors (P > .05).

Our study with a large cohort of Asian patients showed that the prevalence of benign lesions was similar to previously reported Western studies. However, the most common benign lesion was angiomyolipoma, compared with oncocytoma in Western countries. The results of this study may help clinicians counsel female and younger patients recently diagnosed with small renal masses and decide the most appropriate treatment, including renal biopsies and close observation.