Original ArticlesRenal Leiomyoma A Contemporary Multi-institution Study of an Infrequent and Frequently Misclassified NeoplasmPatil, Pallavi A. MD*; McKenney, Jesse K. MD*; Trpkov, Kiril MD†; Hes, Ondrej MD‡; Montironi, Rodolfo MD§; Scarpelli, Marina MD§; Nesi, Gabriella MD∥; Aron, Manju MD¶; Sangoi, Ankur R. MD#; Gattuso, Paolo MD**; Magi-Galluzzi, Cristina MD, PhD*Author Information *Robert J. Tomsich Pathology and Laboratory Medicine Institute, Cleveland Clinic, Cleveland, OH ¶Keck School of Medicine, University of Southern California, Los Angeles #Department of Anatomic Pathology, El Camino Hospital, Mountain View, CA **Department of Pathology, Rush University Medical Center, Chicago, IL †Department of Pathology and Laboratory Medicine, University of Calgary and Calgary Laboratory Services, Calgary, AB, Canada ‡Department of Pathology, Medical Faculty and Charles University, Pilsen, Czech Republic §Department of Pathology, University of Ancona, Ancona, Italy ∥Department of Pathology and Oncology, University of Florence, Firenze, Italy Conflicts of Interest and Source of Funding: The authors have disclosed that they have no significant relationships with, or financial interest in, any commercial companies pertaining to this article. Correspondence: Cristina Magi-Galluzzi, MD, PhD, Robert J. Tomsich Pathology and Laboratory Medicine Institute, Cleveland Clinic, 9500 Euclid Avenue, L25, Cleveland, OH 44195 (e-mail: [email protected]). The American Journal of Surgical Pathology: March 2015 - Volume 39 - Issue 3 - p 349-356 doi: 10.1097/PAS.0000000000000354 Buy Metrics Abstract Renal leiomyoma is an exceptionally rare benign mesenchymal tumor of the kidney predominantly arising in proximity of the renal capsule or pelvis. Its rarity and nonspecific clinical and imaging features may lead to radical or partial nephrectomy on the basis of preoperative suspicion of renal cell carcinoma. The diagnosis of renal leiomyoma is challenging because of the histologic overlap with lipid-poor angiomyolipoma (AML). We conducted a multi-institution study to characterize renal leiomyoma in greater detail. We collected and reviewed 24 cases diagnosed initially as renal leiomyoma in 10 institutions from North America, Canada, and Europe. Immunohistochemical expression of desmin, HMB-45, estrogen receptor (ER), progesterone receptor (PR), and cathepsin K was evaluated. Upon central review, 9 tumors were classified as renal leiomyoma, whereas the remaining were reclassified as AML (n=13), myolipoma (n=1), and medullary fibroma (n=1). All renal leiomyomas were solitary and occurred in female patients (mean age 63 y; range, 44 to 74 y). Tumor size ranged from 0.6 to 7.0 cm (mean 2.9 cm); 7 originated from the renal capsule or the subcapsular area and 1 from a large vessel in the renal sinus. All leiomyomas were diffusely positive for desmin and negative for HMB-45 and cathepsin K; 6/9 (67%) showed diffuse ER and PR expression, and 1 case showed focal ER positivity only. Renal leiomyoma should be included in the histologic differential diagnosis of solid renal masses, particularly in perimenopausal women. The main differential diagnosis is with lipid-poor AML, and cathepsin K plays a key role in distinguishing these 2 lesions. Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.