Incidence of benign pathologic lesions at partial nephrectomy for presumed RCC renal masses: Japanese dual-center experience with 176 consecutive patients

OBJECTIVES To determine the incidence of benign pathologic findings at elective partial nephrectomy for renal masses thought to be renal cell carcinoma (RCC) on preoperative imaging in Japanese patients. METHODS From 1993 to 2007, 176 patients (46 women and 130 men) underwent elective partial nephrectomy for presumed RCC masses in 2 Japanese centers. The mean size of the resected lesions was 2.3 cm (range 0.3-5.8). Overall, 97 and 79 patients had a renal mass of <= 2 cm and > 2 cm, respectively. Of the 176 patients, 100%, 89%, and 32% had preoperatively undergone computed tomography, ultrasonography, and magnetic resonance imaging, respectively. RESULTS Of the 176 masses resected, the pathologic examination revealed benign findings in 19 (11%), angiomyolipoma in 10 (5.7%), oncocytoma in 5 (2.8%), complicated cysts in 2 (1.1%), and a solitary fibrous Winor and scar of the kidney I each (0.6%). Of the 46 women, 12 (26.1%) had benign lesions compared with 7 of the 130 men (5.3%; P = .0003). Of the 10 angiomyolipomas diagnosed, 8 were diagnosed in women (P = .0004). Tumor size was not associated with benign histologic findings. The incidence of benign lesions was equivalent (10% and 12%) between the 2 centers. CONCLUSIONS The present incidence (11%) of benign lesions in presumed RCC masses at surgery in Japanese patients was lower than the incidence of 20%-30% previously reported from Western countries, probably because of the low incidence of oncocytomas in Japanese patients. Women had almost 5 times the likelihood of having a benign lesion compared with men, because of the high incidence of angiomyolipomas in women.