Mixed Epithelial and Stromal Tumor of the Kidney and Cystic Nephroma Share Overlapping Features Reappraisal of 15 Lesions Tatjana Antic, MD; Kent T. Perry, MD; Kathleen Harrison, PhD; Polina Zaytsev, MD; Michael Pins, MD; Steven C. Campbell, MD, PhD; Maria M. Picken, MD, PhD c Context.ÐCystic nephroma is a rare cystic tumor, which and smooth muscle differentiation was con®rmed by elec- only recently has been recognized as an exclusively adult tron microscopy. In mixed epithelial and stromal tumors of lesion. Mixed epithelial and stromal tumor of the kidney is the kidney, the stroma was positive for estrogen and pro- also a rare, recently recognized, biphasic tumor composed gesterone receptors in 4 of 5 lesions tested. In cystic ne- of tubular and cystic elements embedded in grossly rec- phroma, focal positivity for hormone receptors was seen ognizable spindle cell stroma. The histogenesis of both le- in 2 of 7 tumors tested; both positive lesions were from sions is unclear. women. The epithelial lining in both mixed epithelial and Objectives.ÐTo compare clinical phenotype, morphol- stromal tumor of the kidney and cystic nephroma lesions ogy, and immunohistochemistry in mixed epithelial and was variable with regard to shape, cytoplasmic appear- stromal tumor of the kidney and cystic nephroma in order ance, and immunophenotype (with focal positivity for to explore the relationship between these 2 lesions. CD10, cytokeratin 7, high-molecular-weight keratin, and Design.ÐFifteen biphasic lesions (8 mixed epithelial and Ulex europaeus detectable in both lesions). This pattern stromal tumors of the kidney and 7 cystic nephromas) were suggests variable differentiation, which was con®rmed by studied. All cases were reviewed and subjected to detailed electron microscopic studies (performed in 1 case). pathologic studies, and the results were correlated with Conclusions.ÐWhile mixed epithelial and stromal tumor clinical ®ndings. of the kidney has a strong association with the female sex Results.ÐMixed epithelial and stromal tumor of the kid- and hormonal milieu, cystic nephroma can affect both sex- ney occurred exclusively in women aged 36 to 80 years es and, on occasion, may also have hormonal associations. (mean, 49.7 years), all of whom had a history of estrogen Morphologically, there is considerable overlap between therapy and/or obesity. Cystic nephroma occurred in both both lesions, which suggests that they may represent op- sexes; patients were aged 22 to 71 years (mean, 50.4 posite ends of the spectrum of the same process. Our stud- years), and a history of hormonal therapy was present on ies also suggest that the tubules may be entrapped rather occasion. All 15 lesions were benign. Lesions varied by than comprising an intrinsic component of the tumor. size, the proportion of cystic component, and the amount However, further studies, including molecular studies, are and cellularity of stroma. However, in all lesions tested, needed to support this hypothesis. the stroma was diffusely positive for smooth muscle actin, (Arch Pathol Lab Med. 2006;130:80±85) ystic nephroma (CN) features cysts lined by hobnail agnostic criteria for CN as ``an entirely cystic lesion with C or attenuated epithelium, thin septa containing loose no grossly recognizable expansile stroma.'' These authors stroma with ®broblasts and, focally, cells resembling also recognized clinical differences between pediatric and smooth muscle. This uncommon lesion, also termed mul- adult cystic lesions, which subsequently paved the way for tilocular cyst and multilocular cystic nephroma, was earlier the acceptance of CN as an exclusively adult entity. Thus, diagnosed in both adults and children. The concept of CN lesions described earlier as CN in children are now con- has been evolving. In 1998, Eble and Bonsib1 de®ned di- sidered to belong to the spectrum of nephroblastoma and are, therefore, biologically different from morphologically similar lesions found in adults. Accepted for publication September 1, 2005. The term mixed epithelial and stromal tumor of the kidney From the Departments of Pathology (Drs Antic, Harrison, and Picken) 2 and Urology (Drs Perry and Campbell), Loyola University Medical Cen- (MEST) was ®rst introduced by Michal et al in 1998 to ter, Maywood, Ill; Department of Pathology, West Suburban Medical describe a biphasic cystic lesion with grossly recognizable Center, Oak Park, Ill (Dr Zaytsev); and Department of Pathology, North- stroma in a middle-aged woman. In the past, other names, western University, Chicago, Ill (Dr Pins). such as cystic hamartoma of the renal pelvis3±6, or adult meso- The authors have no relevant ®nancial interest in the products or blastic nephroma,7±9 were applied to such lesions. However, companies described in this article. Reprints: Maria M. Picken, MD, PhD, Department of Pathology, Loy- it is now believed, based on molecular studies, that MEST ola University Medical Center, Building 110, Room 2242, 2160 S First has no relationship to mesoblastic nephroma.10 In 2000, Ave, Maywood, IL 60153 (e-mail: [email protected]). Adsayetal11 published a series of 12 MEST tumors and 80 Arch Pathol Lab MedÐVol 130, January 2006 Overlapping Features of Biphasic Renal TumorsÐAntic et al Table 1. Summary of Clinicopathologic Data Hormonal Case No. Age, y/Sex Tumor Location Tumor Size, cm Clinical History Therapy Diagnosis* 1 45/F Cortex 2 Metastatic breast carcinoma 1 MEST 2 53/F Cortex 0.5 Metastatic breast carcinoma, obesity 1 MEST 3 80/F Cortex 0.8 Coronary artery disease, obesity 1 MEST 4 58/F Cortex 2.2 Hysterectomy 2 MEST 5 36/F Renal pelvis 3 Obesity 2 MEST 6² 43/F Cortex 1.7 Hematuria, ovarian cyst 1 MEST 7 40/F Renal Pelvis 3 Unknown 1 MEST³ 8 43/F Cortex 10 Oophorectomy, obesity 2 MEST³ 9 29/F Cortex 3 Unknown 2 CN 10 64/F Cortex 3 Asthma, obesity 1 CN 11 71/F Cortex 8.5 Diabetes, colon cancer 2 CN 12 58/M Cortex 1.4 Unknown 2 CN 13 47/M Cortex 1.4 Renal carcinoma 2 CN 14 22/M Cortex 9 Unknown 2 CN 15 62/M Cortex 7.4 Unknown 2 CN * MEST indicates mixed epithelial and stromal tumor of the kidney; CN, cystic nephroma. ² Electron microscopic study performed. ³ Original diagnosis was cystic nephroma. noted that MEST tumors tend to occur in middle-aged RESULTS and older women; the majority of patients had a history After review of 15 biphasic lesions, 8 lesions were clas- of estrogen therapy. While some patients present with si®ed as MEST and 7 as CN. Two diagnoses were changed ¯ank pain and hematuria, many lesions are discovered from CN to MEST. One lesion, which was originally di- incidentally during workup for other conditions unrelated agnosed in 1989 as CN, represented a classic example of to the kidney. a solid and cystic lesion now recognized as MEST (case With this recent recognition of MEST, it is becoming 7). Another recent case (case 8), a predominantly cystic, clear that the histogenesis and diagnostic criteria for bi- large (10.0 cm) lesion, was initially classi®ed as CN; how- phasic renal tumors are not well de®ned, and within the ever, after review, it is now considered to be a MEST le- published series of both MEST and CN are lesions that sion. show overlap between the 2 entities.1,12 The issue of a re- lationship between MEST and CN has only recently been Mixed Epithelial and Stromal Tumors of the Kidney 12 addressed. The purpose of this study was to compare The 8 MEST cases (Table 1, cases 1±8) occurred exclu- clinical phenotype, morphology, and immunohistochem- sively in women aged 36 to 80 years, with a mean age of istry in MEST and CN in order to explore the relationship 49.7 years. Five patients had a long-term history of estro- between these 2 lesions. gen therapy; 4 patients were obese, 2 of whom had met- MATERIALS AND METHODS astatic breast carcinoma. Three patients died of unrelated diseases, and MEST was an incidental ®nding on autopsy The ®les of 3 institutions were searched for biphasic lesions of (cases 1±3). One patient (case 6) presented with hematuria. the kidney. From 1989 to 2004, 15 cases were identi®ed that met the criteria of CN and/or MEST and were therefore included in All other lesions were discovered incidentally. this study (Table 1). Slides were reviewed and diagnoses veri®ed Grossly, all MEST lesions were well-circumscribed. Sev- according to the World Health Organization (2004) diagnostic cri- en lesions had abundant solid stroma involving more than teria for MEST and CN.13 Only patients older than 20 years were 50% of the tumor volume; all of these lesions measured 3 included in the study. Two cases of CN were reclassi®ed as cm or less. One large tumor (10.0 cm, case 8) was grossly MEST, subsequent to review; the original diagnoses of CN were predominantly cystic, with stroma occupying less than con®rmed in the remaining cases. There were 8 MEST lesions (5 30% of the tumor volume. All except for 2 small lesions surgical and 3 autopsy specimens) and 7 CN cases. In cases 2 (cases 2 and 3) showed cystic features. Tumor size ranged and 3, only limited immunohistochemical studies were possible from 0.5 cm to 10.0 cm, with an average size of 2.9 cm. due to the small size of the lesions. In case 7, only hematoxylin- eosin±stained slides were available for review. Electron micro- Six tumors involved cortex, with the 2 smallest lesions scopic studies of the epithelial component in case 6 were pub- being entirely surrounded by cortex. Two tumors pro- lished previously.14 The tissue was ®xed in formalin, processed truded into the renal pelvis, but no communication with for microscopic examination in paraf®n blocks, and stained with the renal pelvis was present (Table 1).