Adult mesoblastic nephroma: expansion of the morphologic spectrum and review of literature

Mixed epithelial and stromal tumor (MEST) in a young adult male: A case report and literature review

Introduction and importance

A MEST is a rare renal tumor, with stromal as well as epithelial components. It is predominantly benign and local recurrence is not very common. In the majority of the cases, it occurs in females. Its occurrence in a young male makes it a rarity.

Case presentation

A 24 years old male presented at SIUT with the complaint of left flank pain on and off for one month. CT scan showed soft tissue density mass in left renal pelvis extending from mid-pole calyces to pelviuretric junction, leading to obstruction and ultimately mild uropathy. We found a partially obstructing staghorn calculus with asymmetrical cortical thinning. Left Robot-Assisted Nephro-ureterectomy plus excision of bladder cuff was planned in which 3 × 4 cm mass involving the left renal pelvis was excised. To date, there is no radiologic evidence of disease recurrence.

Clinical discussion

MEST in young adults is an extremely rare tumor. They have been referred to by many alternate synonyms including 'adult mesoblastic nephroma' and 'cystic nephroma' with 'ovarian' or 'cellular' type stroma. Majority of patients with MEST present, with hematuria, abdominal pain, palpable flank mass, recurrent urinary tract infections. Similarly, our patient presented initially with nonspecific pain in the left flank region. Majority of cases in the literature presented with the tumor in benign stage, with localized spread, and without recurrence.

Conclusion

Mixed epithelial and stromal tumors (MEST) of the kidney are distinct entities of benign kidney tumors. MEST in young males is a very rare entity, and a small number of cases exist. Histopathology plays a very cardinal role in diagnosis, and overall the disease has a promising outcome with conservative surgery.

Bilateral and multiple mixed epithelial and stromal tumors of the kidney: A case report

Mixed epithelial and stromal tumor (MEST) of the kidney is a benign tumor occurring predominantly in older women. Histologically, MEST comprises tubuloglandular and cystic structures in an ovarian-like stroma. Bilateral and multiple cases are rare. We herein present a case of bilateral and multiple MEST in a 43-year-old woman. The patient presented with gross hematuria and was referred to a primary care physician. A computed tomography scan revealed 5 tumors in the right and 2 in the left kidney. Renal cell carcinoma was suspected, and left partial nephrectomy followed by right radical nephrectomy was planned. After the left partial nephrectomy, the histopathological diagnosis was MEST, which was consistent with the results obtained following needle biopsy. Therefore, the contralateral tumor was also suspected to be MEST, and needle biopsy was performed. The histopathological diagnosis was identical and the right kidney was spared. The patient is currently periodically monitored. As MEST is a benign tumor, preoperative diagnosis is crucial for avoiding overtreatment.

Mixed Epithelial and Stromal Tumor of the Kidney: A Clinicopathologic Study of 53 Cases

Mixed epithelial and stromal tumor of the kidney is an uncommon complex neoplasm, and previous studies have included only a modest number of cases and have left gaps in our understanding of its morphology. We analyzed 53 tumors (46 F, median age: 49 y), collecting data on gross, histologic, and immunohistochemical features. The most common gross appearance was solid and cystic (47%). Hypocellular fibrous and cellular spindle cell stroma were the most common stromal types, followed by smooth muscle differentiation, edematous stroma, and adipose tissue. Hypocellular fibrous stroma and adipose tissue were more common in larger tumors (P=0.003 and 0.04, respectively) and cellular spindle cell stroma in smaller tumors (P=0.0009). Combinations of diverse stromal elements were common: roughly 50% of tumors contained >4 types of stroma. With regard to epithelium, tiny crowded and branching glands were present in 60% of tumors. Round glands lined by tall cuboidal epithelium, reminiscent of thyroid follicles, spatulate papillae reminiscent of phyllodes tumor, glands reminiscent of nephrogenic adenoma, and complex papillae were also frequently found. Combinations of diverse epithelial elements were common: 64% of tumors contained >4 types of epithelium. All of the tumors except 1 were positive for smooth muscle actin in the stroma. Desmin and caldesmon expression were more variable. Stains for progesterone and estrogen receptors showed positivity in the stromal component in 85% and 73% of tumors, respectively. CD10 and CD34 immunolabeling were restricted to pericystic spindle cells. No tumor expressed inhibin. In summary, this study demonstrates a strong tendency for mixed epithelial and stromal tumors to contain multiple types of stroma and epithelium and comprehensively analyzes the immunohistochemical profile.

Congenital mesoblastic nephroma 50 years after its recognition: A narrative review

Congenital mesoblastic nephroma (CMN) is a rare pediatric renal tumor with low malignant potential that most commonly occurs early in infancy. Treatment strategies are based on the few published CMN series, while a significant number of CMN patients have been described in case reports. The aim of this narrative review was to create an up-to-date overview of the literature. Complete surgical removal is curative in most cases. The risk of treatment-related mortality (both surgery- and chemotherapy-related) is relatively high in the first weeks of life, indicating that these young patients deserve special attention with respect to timing and type of treatment.

Mixed epithelial and stromal tumors of the kidney discovered incidentally at autopsy

Mixed epithelial and stromal tumors (MEST) of the kidney are uncommon neoplasms that were added to the World Health Organization's renal tumor classification in 2004. These entities are biphasic and contain both epithelial and mesenchymal components. MEST most commonly occur in women. Presented are two cases of MEST incidentally discovered at autopsy.

Multiphasic contrast-enhanced CT and MRI findings of adult mesoblastic nephroma: A report of two cases

Mesoblastic nephroma (MN) presenting in an adult is extremely rare. The computed tomography (CT) and magnetic resonance imaging (MRI) features of this tumor in adulthood have not been widely reported. We present two additional cases of adult MN and describe the multiphasic contrast-enhanced CT and MRI findings.

Mixed epithelial and stromal tumor of the kidney (MEST) simulating an upper tract TCC

We present a rare and interesting case of a mixed epithelial and stromal tumour (MEST) of the kidney. The case is unique as it involves a male patient with no history of hormonal therapy presenting with a filling defect in the renal collecting system and positive urine cytology. The patient was diagnosed with transitional cell carcinoma of the renal pelvis and subjected to nephroureterectomy, which revealed a solid tumour arising from the lower calyces and extending into the renal pelvis and upper ureter. Pathology revealed a MEST. The patient was disease-free at the 6-month follow-up.

Mixed epithelial and stromal tumors of the kidney: an overview

Mixed epithelial and stromal tumor of the kidney is a recently recognized distinct neoplasm that should be distinguished from other renal neoplasms. These tumors are relatively rare with a female preponderance. Imaging studies are not diagnostic but reveal a solid or solid and cystic mass in most cases. Histopathologically, these tumors reveal biphasic growth pattern comprising mesenchymal and epithelial elements with characteristic estrogen and progesterone receptor immunoreactive mesenchyme reminiscent of ovarian stroma. Malignant transformation, recurrence, and metastasis are rare; however, recently a few cases of malignant mixed epithelial and stromal tumors have been reported in the literature. Recently a case with translocation t(1;19) has been described. This article provides a brief overview of the current knowledge of mixed epithelial and stromal tumor of the kidney.

Adult cystic nephroma and mixed epithelial and stromal tumor of the kidney are the same disease entity: molecular and histologic evidence

Adult cystic nephroma (CN) and mixed epithelial and stromal tumor of the kidney (MEST) are considered as separate entities in the 2004 World Health Organization classification of renal neoplasms. Recent studies suggested that the two share clinicopathologic features and may represent the same disease process of varying morphology. However, definitive genetic evidence is lacking. We examined their relationship using gene expression profiling and histologic analysis. Gene expression profiles of 3 CN and 3 MEST were analyzed using HGU133 Plus 2.0 microarrays (Affymetrix) and were compared with each other and also with 48 other renal tumors and 13 normal kidneys. Histologic examination of 26 CN and 13 MEST focused on the cystic septal thickness, cyst-to-stroma ratio, stromal cellularity and composition, types of epithelial cells lining cysts and glands, and estrogen and progesterone receptors expression. Patients' age, sex distribution, and tumor size were similar between the two. They also shared many histologic features, including lining epithelium of cysts and glands, stromal cellularity and composition. Unsupervised clustering of mRNA expression profiles demonstrated that they had very similar expression profiles that were distinct from other renal tumors. By microarray analysis, progesterone receptor expression was significantly higher in CN and MEST relative to both normal and other renal tumors, while estrogen receptor expression was not. By immunohistochemistry, expression of both receptors was similar between CN and MEST. This study provides the most convincing molecular evidence that CN and MEST represent different parts of the morphologic spectrum of the same disease.

Mixed epithelial and stromal tumor of kidney with malignant transformation: report of two cases and review of literature

We present 2 cases of mixed epithelial and stromal tumor of the kidney with sarcomatous transformation. One patient was a 53-year-old woman who presented with macroscopic hematuria. The resected tumor involved the right renal parenchyma, measuring 13.0 x 8.0 x 4.0 cm, and extended to perirenal adipose tissue. The second patient was a 56-year-old woman who presented with right flank colic pain. The tumor measured 6.0 x 5.5 x 4.0 cm, with an intact capsule at the upper pole. Both tumors showed a well-circumscribed, multilocular, cystic, and focally solid mass. Sections of both tumors revealed benign and malignant components. The benign component consisted of multilocular cysts and fibrous stroma with a focally ovarian stromalike component. The malignant component in both cases was predominantly composed of undifferentiated cellular spindle cell sarcoma with frequent mitoses. One case showed additional heterologous malignant elements, including rhabdomyosarcomatous, chondrosarcomatous, and focal carcinomatous components. We report 2 additional cases of sarcomatous transformation in mixed epithelial and stromal tumor of the kidney.

Renal tumours of childhood: an update

The role of the pathologist has been fundamental in the progress of the treatment of paediatric renal tumours. There are different philosophies in the treatment of these tumours, and there have been many recent advances in the areas of chemotherapy, identification of new entities, prognostic histological criteria following treatment and molecular prognostic and diagnostic features. This review discusses the different approaches of the different treatment protocols from Europe and North America, and reviews staging criteria, prognostic criteria and also the different tumour entities.

Fat-predominant mixed epithelial stromal tumor (MEST): report of a unique case mimicking angiomyolipoma

A unique case of a mixed epithelial stromal tumor (MEST) that was predominantly composed of adipose tissue is reported here. Radiographically and grossly, the lesion was thought to be an angiomyolipoma, based upon its fatty appearance. Microscopically, the lesion was predominantly composed of mature adipose tissue but also contained clusters of bland tubules surrounded by smooth muscle bundles and collagen. By immunohistochemistry, the stroma labeled diffusely for estrogen and progesterone receptors, while the muscle bundles labeled for desmin. Melanocytic markers HMB45 and Melan A, typically positive in angiomyolipoma, were nonreactive. This case expands the morphologic spectrum of MEST to include mimics of angiomyolipoma.

Recently Described and Emphasized Entities of Renal Neoplasms

Context.—Recent advances of molecular biology and cytogenetics of renal cancer have resulted in the new classification of renal neoplasms and a number of subtypes are identified and emphasized. In addition, rare nonepithelial renal neoplasms are identified and characterized. Familiarity with these entities will help make the most accurate diagnosis and guide the treatment and follow-up of patients with renal neoplasm.

Objective.—To review the clinicopathologic entities of renal neoplasms that are recently defined or emphasized. Their clinical, gross, microscopic, and immunohistochemical features, as well as specific cytogenetic or molecular abnormalities, are discussed. Important differential diagnoses of each entity are also briefly discussed.

Data Sources.—Extensive review of published literature and our experience.

Conclusions.—A number of new entities of renal neoplasms or genetically defined renal cell carcinomas have been identified or emphasized because of their unique genetic or molecular changes. Recognition of these entities becomes important as some of them have different biologic behavior and treatment strategies may be different.

Cystic nephroma and mixed epithelial and stromal tumor of kidney: a detailed clinicopathologic analysis of 34 cases and proposal for renal epithelial and stromal tumor (REST) as a unifying term

Cystic nephroma (CN) and mixed epithelial and stromal tumor (MEST) are rare benign renal neoplasms that have overlapping clinical and morphologic features, including predominance in middle-aged women, variably cystic architecture, eosinophilic cells, and hobnail cells lining the cysts and ovarian-type stroma. The aim of this study was to analyze and compare the histologic features and immunohistochemical profile of these tumors. We studied 34 cases from 5 large academic institutions. Twenty tumors were diagnosed as CNs, 18 in women and 2 in men, their age ranged from 24 to 63 (mean 48; median 50) years. Fourteen tumors were diagnosed as MESTs, all in women, their age ranged from 26 to 84 (mean 52; median 51) years. Histologically, all tumors were well-circumscribed except for one MEST. The stromal/epithelial ratio was approximately 2.3 in MESTs versus 0.3 in CNs; cellular ovarian-type stroma composed 45% of the stroma in MESTs and 12% of the stroma of CNs. Stromal hyalinization was prominent in both. Five MESTs showed stromal luteinization. In the epithelial component, the relative amount of large cysts, medium to small cysts, and phyllodes-type glands was: 65%/25%/10% in CNs versus 25%/40%/35% in MESTs. The epithelial component ranged from flat to cuboidal to hobnail cells in both types of tumors. No significant atypia of either component was seen, although the epithelial cells showed reactive changes. Immunohistochemical stains for estrogen receptors and progesterone receptors showed 62% and 85% positivity in the stromal component of MESTs versus 19% and 40% in CNs. CD10 positivity was seen in 77% of MESTs versus 50% of CNs, calretinin was seen in 69% of MESTs versus 41% of CNs, and inhibin in 42% of MESTs versus 36% of CNs, although the staining was focal. Follow-up in both categories of tumors (mean 3.2 y, median 3 y for CNs and mean 2.5 y, median of 2 y for MESTs) showed no evidence of recurrence or metastases in keeping with their benign nature. This study highlights the remarkable similarity between CN and MEST in sex predilection, age distribution, and morphologic attributes of both the epithelial and stromal components and immunohistochemical profile albeit with variation in individual categories with higher prevalence of stromal to epithelial ratio, prominent ovarian stroma, smaller cysts with phyllodes glands pattern and stromal luteinization being more common in MEST; and large cysts, thin septae and low stromal to epithelial ratio in CN. The presence of ovarian-type stroma and müllerian related immunohistochemical markers raises the possibility that these tumors may originate from müllerian remnants misplaced during embryogenesis. On the basis of detailed morphologic analysis of this series of CN and MEST, we propose a unifying term of "renal epithelial and stromal tumor" (REST) to encompass the spectrum of findings observed in these tumors at least until new molecular studies can prove or disprove this challenging hypothesis.

Mixed epithelial and stromal tumor of the kidney: a case report

The descriptive term "mixed epithelial and stromal tumor of the kidney" was recently proposed for a group of renal tumors characterized histologically by a mixture of stromal and epithelial proliferation. It is a rare benign neoplasm of the kidney which has been reported under various names such as adult type mesoblastic nephroma or others. We report a case of mixed epithelial and stromal tumor in a 47 yr old female patient presenting as a partly cystic and partly solid renal mass. Microscopically, the tumor exhibited spindle cell component in solid portion and epithelial proliferation around microcystic areas. Immunoreactive profiles and ultrastructural examination suggested myofibroblastic nature of the stromal cells. We believe this case exemplifies a unique adult renal tumor displaying both epithelial and stromal neoplastic component and has a few unusual features worthy of attention.

Cystic angiomyolipoma of the kidney: a clinicopathologic description of 11 cases

This report deals with 11 examples of renal angiomyolipomas (AML) which appear to include an epithelial element as a part of the neoplasm in the form of gross or microscopic cysts-usually both. There were seven females and four males between the ages of 20 and 70 years with mean age of 45 years. Three of these were known to be symptomatic: intermittent flank pain and gross hematuria for 2 months; recurrent hematuria both before and after flank trauma and a third patient with acute abdomen due to a ruptured tumor blood vessel. Cysts were described in three of the six cases where radiographic data were available. Seven tumors were in the right kidney and four in the left. In gross descriptions, cysts were mentioned in seven and they ranged from 6.0 to 2.0 cm with a median and mean maximal diameter of 5.0 and 4.0 cm, respectively. Microscopically, virtually all of the tumors included multiple smaller cysts and these were lined by flat, cuboidal or columnar epithelium and occasionally hobnail epithelium. There was usually a subepithelial collar of poorly differentiated cells, but the solid element of all tumors was myomatous angiomyolipoma; only one case had any adipose tissue. A dominant histological feature was the prominent lymphatic channels-identical to those of lymphangiomyomas and myomatous or triphasic AMLs. They are much more conspicuous in these cystic cases. Immunohistochemically, all tumors tested were reactive with actin, desmin and HMB-45, with the latter being more intensely positive in the subepithelial collars. Estrogen and progesterone receptors were usually positive, also. The behavior of these lesions appears to be no different from that of other AMLs.

Benign mixed epithelial and stromal tumor of the kidney: imaging findings

Three cases of mixed epithelial and stromal tumor of the kidney with their imaging findings are described; these cases have not been reported previously in the radiology literature. This benign tumor contains epithelial and spindle cell stromal components and arises exclusively in adult women. It is characterized morphologically by a solid and cystic nature with delayed enhancement.

Mixed epithelial and stromal tumor of the kidney in a 12-year-old girl

Mixed epithelial and stromal tumor of the kidney (MESTK) is a rare kidney neoplasm that almost exclusively occurs in perimenopausal women, and long-term estrogen replacement is relevant to its pathogenesis. Herein is described an atypical case of MESTK uncovered in a 12-year-old premenarcheal girl without a history of prior estrogen use. On surgical specimen it was found that the well-circumscribed tumor measuring 14 cm arose from the lower pole of the right kidney, showing solid and fibrous-cystic areas. Microscopically, it was composed both of epithelial structures similar to renal tubules and stroma comprising non-specific spindle cells. Some intratumoral tubules showed affinities to distal-nephron-specific lectins, and those immunoreactive for proximal-tubule-specific CD15 were also present. In addition, primitive ductal structures were reactive both for CD15 and lectins, but immature epithelial elements typical of nephroblastoma were absent. Spindle cells were positive for actin, desmin and vimentin, and expressed progesterone and estrogen receptors. The tumor was comparable with MESTK, although some epithelia were associated with the immunophenotype of proximal tubules. The patient was free of disease postoperatively for 40 months. In the present case, remnants of the primitive periductal mesenchyme might be promoted to neoplastic cells by a sex-steroid surge during puberty.

Incidental Stromal-Predominant Mixed Epithelial-Stromal Tumors of the Kidney: A Mimic of Intraparenchymal Renal Leiomyoma

Context.—Mixed epithelial-stromal tumor of the kidney is a recently recognized benign renal tumor that usually occurs in adult women and typically forms a sizable lesion with solid and cystic areas. The recognized morphologic spectrum of this recently described entity is evolving.

Objective.—To review the clinicopathologic features of 3 small mixed epithelial-stromal tumors of the kidney that were incidental findings in kidneys removed for other reasons.

Design.—The clinical presentation and morphologic findings of the 3 cases were reviewed. A panel of immunohistochemical stains was performed.

Setting.—Academic medical center.

Results.—All 3 lesions contained predominantly fascicles of smooth muscle mimicking leiomyoma, but they also had cellular subpopulations of smaller, müllerian-appearing stromal cells. Tubules present within the lesion were most abundant at the periphery, suggesting that they might be entrapped. Although only the spindled smooth muscle cells were immunoreactive for muscle markers desmin and actin, both the spindled smooth muscle cells and the cellular müllerian-appearing stromal cells demonstrated diffuse nuclear labeling for estrogen and progesterone receptors.

Conclusions.—Mixed epithelial-stromal tumor of the kidney may present as an incidental stromal-predominant lesion within the kidney. Such lesions are easily confused with leiomyomas or stromal-predominant angiomyolipomas.

Tubulocystic Carcinoma, Mucinous Tubular and Spindle Cell Carcinoma, and Other Recently Described Rare Renal Tumors

In the past 10 years, several new renal tumors have been identified. Some have been reviewed in this article, and others have been reviewed elsewhere in this issue. Most have been included in the 2004 edition of the WHO classification of tumors of the urinary system and male genital organs. Tubulocystic carcinoma needs to be studied and characterized more fully.

Calcium Oxalate Deposition in Renal Cell Carcinoma Associated With Acquired Cystic Kidney Disease

The main complication of acquired cystic kidney disease (ACKD) is frequent development of renal tumors, including renal cell carcinoma (RCC). Intratumoral deposition of calcium oxalate (CaOx) is a distinct feature of ACKD-associated RCCs, but several features of this type of RCC are not known. Features of the 30 end-stage renal disease (ESRD)-associated RCCs identified within a 13-year period, including eight with CaOx deposition, were analyzed. Pathologic and clinical features of CaOx positive (+) and negative (-) RCCs were evaluated and compared. The CaOx+ RCCs showed higher tendency for bilaterality and multifocality. Seven tumors displayed distinctive morphologic features characterized by tumor cells with ill-defined cell membrane, abundant granular eosinophilic cytoplasm, large nuclei, and prominent nucleoli. One tumor was of clear cell type. Regardless of histologic type, all tumors displayed a proximal tubular differentiation. No significant difference was noted for tumors' stage, proliferation, and apoptosis rate between the CaOx+ and CaOx- RCCs. CaOx+ RCCs account for a significant portion of all ESRD-associated RCCs. The majority of these RCCs display a distinctive morphologic profile. Proximal tubular cell differentiation in conjunction with ESRD-mediated high serum level may be pathogenetically important for intratumoral CaOx deposition. These RCCs seems to have a relatively good prognosis.

Cystic Nephroma: A Histologic and Immunohistochemical Study of 10 Cases

Context.—Cystic nephroma is a rare and controversial benign multicystic renal tumor. While the clinical, radiologic, and histologic features of cystic nephroma are well described, the immunohistochemical features are not. The role of immunohistochemistry in the differential diagnosis, which includes multicystic renal cell carcinoma, is also unknown.

Objective.—To define the histologic and immunohistochemical features of cystic nephroma.

Design.—Ten cases of cystic nephroma diagnosed at 2 institutions during a period of 10 years were stained with an immunohistochemical panel consisting of 20 immunostains.

Results.—Median age at diagnosis was 61 years, with a range from 31 to 79 years. The female-to-male ratio was 9:1. Grossly, the tumors were multicystic masses without solid nodules. Histologic features included cysts lined by flat, cuboidal, or hobnail epithelium and septa variably lined by fibrous (10/10 cases) and/or ovarian-like (7/10 cases) stroma. Corpus albicans–like acellular hyalinized structures were noted in the septa in 9 of 10 cases. The cyst epithelium showed consistent positivity for distal tubule/collecting duct markers (cytokeratin 19, cytokeratin AE1/AE3, epithelial membrane antigen) and variable positivity for proximal tubule markers (α1-antitrypsin, lysozyme, CD15, CD10). The ovarian-like stroma (present in 7/10 cases) stained positively for progesterone receptors (6/7 cases) and estrogen receptors (4/7 cases).

Conclusions.—Our immunohistochemical findings confirm a previous report of both distal tubule/collecting duct and proximal tubule differentiation in cystic nephroma. Stromal estrogen and/or progesterone receptor positivity in the majority of cases of cystic nephroma is a novel finding.

Adult mesoblastic nephroma: Appearances on magnetic resonance imaging

Mesoblastic nephroma presenting in an adult is extremely unusual. The magnetic resonance imaging (MRI) appearances of this tumor in adulthood have not been widely reported. We present a 55-year-old patient who was diagnosed with this rare neoplasm and describe the MRI findings.

Mixed epithelial and stromal tumors of the kidney. A report of 22 cases

Mixed epithelial and stromal tumor of the kidney (MESTK) is a recently described subset of renal neoplasm that tends to occur in middle-aged and older women and is characterized by a distinctive histological appearance. To further characterize this lesion, we report the clinicopathological and immunohistochemical features of 22 additional cases from our institutional files. Grossly, the tumors ranged in size from 1 cm to 14 cm (mean 6.7 cm), were well circumscribed but unencapsulated, and showed a cystic cut surface. The tumors were composed of a spindle cell proliferation that resembled ovarian stroma, as well as an epithelial component lining the cystic structures, which usually consisted of flat to hobnailed cells typical of collecting-duct epithelium. Areas displaying features of Mullerian differentiation were also documented in 6 cases, including epithelium of endometrioid, tubal, clear cell and squamous cell type as well as one case showing an architecture that closely resembled Mullerian adenofibroma and adenosarcoma. Follow-up in 14 patients (average 4.4 years) showed no evidence of recurrence or metastasis. We believe these tumors represent the renal counterpart of similar mixed epithelial and stromal neoplasms occurring in the biliary tract and pancreas, which is also characterized by cystic structures lined by epithelium, admixed with ovarian-type stroma. The differential diagnosis for these tumors includes cystic nephroma and cystic partially differentiated nephroblastoma, which we believe to represent clinically and morphologically distinct entities from MESTK. In particular, the distinction from cystic nephroma in adult male patients is emphasized, and two cases of this entity are included in the study for comparison.

Hyperparathyroidism-jaw tumour syndrome

Amongst hyperparathyroidism-related syndromes, hyperparathyroidism-jaw tumour syndrome is one of the least common and relatively unknown but its clinical and genetic aspects are not less interesting or important. With the recent identification of its genes, we can now better characterize the disease, both clinically and genetically, which will certainly impact the field of endocrinology and oncology. In this article, we review the clinico-pathological features and genetic basis of this syndrome with the hope that it will create awareness and interest in this disease amongst clinicians and basic scientists.

Renal cystic neoplasms and renal neoplasms associated with cystic renal diseases: pathogenetic and molecular links

Cystic renal neoplasms represent an isolated cystic mass not accompanied by cystic change of the renal parenchyma. Although cystic change may be seen in any type of renal neoplasm, a few (i.e., cystic renal cell carcinoma, cystic nephroma, cystic partially differentiated nephroblastoma, mixed epithelial and stromal tumor) are characterized by constant cystic change that may involve the entire tumor. Cystic kidney disease is characterized by cystic change, which usually involves the kidneys in a bilateral and diffuse pattern, does not create a discreet mass, and is due to hereditary or developmental conditions. Some of the cystic kidney diseases are not known to give rise to renal neoplasm; others such as autosomal polycystic kidney disease or multicystic dysplastic kidney may fortuitously coexist with renal neoplasms. Three conditions (acquired cystic kidney disease, tuberous sclerosis, and von Hippel-Lindau disease) are associated with renal neoplasms with such a high frequency that they are considered preneoplastic. This article reviews the differential diagnoses among cystic neoplasms. It also focuses on the underlying genetic and molecular mechanisms for the relationship between cystic renal diseases and renal neoplasms.

Multicystic congenital mesoblastic nephroma

This report describes an unusual example of congenital mesoblastic nephroma cellular variant that presented in a 1-week-old neonate as a multicystic tumor of the kidney. Extensive pseudocystic cavitation resulted from progressive accumulation of ground substance in a loosely myxoid tissue composed of stellate- and spindle-shaped cells that compressed and infiltrated renal tissue. The cells of the tumor were positive for vimentin and smooth muscle actin. The patient is alive and well 16 years after surgery. Differential diagnosis from segmental cystic dysplasia, cystic intralobar nephrogenic rest, cystic nephroma, cystic partially differentiated nephroblastoma, cystic nephroblastoma, and cystic clear cell sarcoma of the kidney, all of which may present at this age, is discussed.

Mixed epithelial and stromal tumor of the kidney lacks the genetic alterations of cellular congenital mesoblastic nephroma

Mixed epithelial and stromal tumor of the kidney is a recently recognized neoplasm that occurs almost exclusively in perimenopausal women. Because it frequently contains areas of smooth muscle in which epithelial structures are embedded, some have concluded that it is the adult form of congenital mesoblastic nephroma. Others have concluded that the morphology and epidemiology of mixed epithelial and stromal tumor indicate that it is unrelated to congenital mesoblastic nephroma. Although the genetic alterations of mixed epithelial and stromal tumor have not been previously elucidated, much is known about the genetic alterations of cellular congenital mesoblastic nephroma. The present study was undertaken to determine if mixed epithelial and stromal tumors have any of the genetic alterations recognized as typical of cellular congenital mesoblastic nephroma. RNA extraction was performed on formalin-fixed, paraffin-embedded tissue from 7 mixed epithelial and stromal tumors followed by reverse-transcription polymerase chain reaction to detect the ETV6-NTRK3 gene fusion. Fluorescent in situ hybridization with centromere-specific probes for chromosomes 8, 11, and 17 was performed to evaluate polyploidy of these chromosomes in 11 cases of mixed epithelial and stromal tumor. None of the mixed epithelial and stromal tumors showed any of these genetic alterations. We conclude that mixed epithelial and stromal tumor of the kidney lacks the genetic alterations typical of cellular congenital mesoblastic nephroma, is unrelated to it, and the appellation "adult mesoblastic nephroma" should not be used for these tumors.

Aspiration cytology of mesoblastic nephroma in an adult: diagnostic dilemma

A case of adult mesoblastic nephroma (MN) was erroneously interpreted as a benign mesenchymal tumor on fine-needle aspiration (FNA) cytology. MN is a rare tumor in infants and is extremely uncommon in adults. A 50-yr-old female presented with a renal lump with the clinicoradiological possibility of renal-cell carcinoma. Giemsa-stained smears were highly cellular and showed cohesive interlacing fragments of spindle cells embedded in abundant pink fibrillary stromal matrix. Epithelial component was seen in the form of tubules. Pleomorphism, mitosis, and necrosis were absent. Cytologic features in both adult and infantile MN are similar, but in an adult can be mistaken for benign or malignant mesenchymal tumor and the sarcomatoid variant of renal-cell carcinoma. FNA in such a rare yet cytomorphologically characteristic lesion can be helpful in guiding the management. Awareness on the part of both the clinician and the cytopathologist is necessary to resolve the diagnostic dilemma.

Primary renal synovial sarcoma: molecular and morphologic delineation of an entity previously included among embryonal sarcomas of the kidney

We report 15 primary renal neoplasms with morphologic, immunohistochemical, and molecular features identical to those of synovial sarcoma. These tumors form a distinct subset of the entity previously designated as embryonal sarcoma of the kidney. Most were diagnosed between the ages of 20 and 50 years. On gross examination, tumors are large, partially necrotic, and usually contain smooth-walled cysts. Microscopically, tumors are characterized by mitotically active, monomorphic plump spindle cells with indistinct cell borders growing in short, intersecting fascicles. Grossly identified cysts are lined by mitotically inactive polygonal eosinophilic cells with apically oriented nuclei ("hobnailed epithelium"). The spindle cells are immunoreactive for vimentin, often immunoreactive for EMA, but typically non-immunoreactive for desmin, actin, S100, or cytokeratins, whereas the cyst epithelium is cytokeratin-positive. These findings are consistent with monophasic, spindled synovial sarcoma encircling dilated native renal collecting ducts. The presence of an SYT-SSX gene fusion resulting from the t(X;18) characteristic of synovial sarcoma was demonstrated by reverse transcriptase polymerase chain reaction in three of three tumors in which adequate RNA could be obtained from paraffin blocks. An additional case demonstrated the characteristic t(X; 18) translocation on cytogenetic analysis, but adequate material to perform molecular studies was not available in this case or the remaining 11 cases. Primary renal synovial sarcoma is a distinctive clinicopathologic entity confirmed by molecular detection of SYT-SSX fusion transcripts.

Adult mesoblastic nephroma with ciliated epithelium. A case report

A case of renal pelvic tumors occurring in a 44-year-old man is reported. There were two polypoid renal pelvic tumors which consisted of glandular and stromal components. Some glands in the tumors had ciliated epithelium and were quite similar to the epididymal tubules. Other glands in the tumors resembled the collecting duct or the mesonephric remnant seen in female genitalia. Immunohistochemistry and electron microscopy revealed smooth muscle differentiation of the stromal cells of these tumors. Some psammoma bodies were seen in the glands of the tumors. We diagnosed these tumors as adult mesoblastic nephroma (MN). The patient has been followed up for 14 months, showing no evidence of recurrence. Differentiation of the tumors from angiomyolipoma, leiomyoma, and nephrogenic adenofibroma is discussed. Adult renal tumors that consist of epithelial and stromal components have been reported under various names. They constitute clinicopathologically different entities originating from pediatric MN. We suggest that these tumors should be termed "adult MN".

Mixed epithelial and stromal tumor of the kidney

We describe the clinicopathologic features of 12 patients with a distinctive tumor of the kidney characterized by a mixture of epithelial and stromal elements that form solid and cystic growth patterns. Similar tumors were reported previously in the literature under various names, including adult mesoblastic nephroma. All but one of the patients were women. The only man had a long history of treatment with lupron and diethylstilbesterol. Seven of the women had histories of long-term oral estrogen use of whom six had undergone total abdominal hysterectomy and bilateral salpingo-oophorectomy several years prior, and the seventh patient had been using oral contraceptives for many years. Another woman had this operation but did not receive any hormone therapy. Ages ranged from 31 to 71 years (mean, 56 yrs). Six patients presented with symptoms, including pain and infections attributable to mass effect, and in six the tumor was detected incidentally. Grossly, the tumors were well-circumscribed (mean size, 6 cm; range, 3-12 cm) and consisted of solid and cystic components, most often in equal proportions but in variable distribution. Microscopically, the spindle cell component ranged in appearance from scar-like fibrous tissue to leiomyoma-like interlacing fascicles; usually there was a mixture of both. More cellular foci reminiscent of ovarian stroma or solitary fibrous tumor were also present. No blastema was present. Epithelial elements (composed of clusters of tubules with variable lining) were scattered amidst the spindle cells, and focally transformed into large cysts lined by cells with abundant pink cytoplasm and a hobnail appearance. Immature epithelial elements typical of Wilms' tumor were not present. Muscle markers (desmin and smooth muscle actin) were positive diffusely and strongly in the spindle cells of all tumors, whereas HMB-45 and CD34 were absent. Estrogen receptors were detected in the nuclei of spindle cells in seven tumors and progesterone receptors in three. The distinctive clinicopathologic characteristics of these lesions warrant their classification as a separate category of kidney tumor. We suggest the descriptive term "mixed epithelial and stromal tumor" for this group until its nature and relationship to other kidney lesions are further clarified. Its preponderance in females with a history of long-term estrogen replacement and the history of long-term sex-steroid use in the only male patient, combined with the frequent content of estrogen and progesterone receptors in the spindle cells, suggest that the hormonal milieu plays a role in the evolution of these tumors. The clinical and pathologic parallels with mucinous cystic tumors of pancreas and liver raise the possibility of a common pathogenetic mechanism that may be linked to the periductal fetal mesenchyme. We think this entity is a benign composite neoplasm in which stroma and epithelium are both integral neoplastic components.

Adult mesoblastic nephroma

We report a case of asymptomatic mesoblastic nephroma in a 54-year-old woman. The tumor showed immunohistochemical reactions similar to developing nephrons. Electron microscopy showed immature tubules with numerous intracytoplasmic intermediate filaments. Recent studies support the concept of pathogenesis of the mesoblastic nephroma originating from collecting ducts. However, this case exhibited a complex pattern of antigenic expression not restricted to the collecting ducts, but including the glycoprotein CD24 and the neural cell adhesion molecule (NCAM). The following differential diagnoses will be discussed: benign mixed epithelial and stromal tumor, metanephric adenoma, and nephrogenic adenofibroma.

Cystic partially differentiated nephroblastoma in an adult: an immunohistochemical, lectin histochemical and ultrastructural study

AIMS

Cystic partially differentiated nephroblastoma (CPDN) is an uncommon renal multicystic tumour, usually affecting early infants. To our knowledge, this report describes the first case of CPDN occurring in an adult.

METHODS AND RESULTS

A 45-year-old man was found incidentally to have a left renal cystic tumour, measuring 20 mm in diameter, at the lower pole far from the pelvis. The tumour was composed of multilocular cystic spaces of variable size and intervening septa without solid nodular areas. The cysts were lined by a single layer of flattened, hobnail, or columnar epithelium. The septa were made of mesenchymal cells, which were admixed with small numbers of loosely aggregated blastemal cells, occasional tubular structures in various stages of development, and a few glomeruloid structures. The tumour cells had no anaplasia, and mitoses were rare. Immunohistochemical and lectin histochemical studies revealed that the cyst lining epithelium and the tubular structures in the septa expressed predominantly the markers for distal tubules and collecting ducts. Ultrastructurally, the cyst lining cells closely resembled collecting duct cells while some tubular structures showed an immature nephrogenic morphology. The patient was alive and well without evidence of recurrence 11 months after surgery.

CONCLUSIONS

CPDN does occur in adults, as experienced in Wilms' tumour, though its incidence is extremely low. This study suggests that CPDN may show maturation intermediate between cystic nephroma and Wilms' tumour, even in adult cases.

Metanephric adenofibroma: report of a case and review of the literature

The recent recognition of a variety of pediatric renal tumors of different biologic behavior places an ever-increasing demand on the surgical pathologist for an accurate diagnosis. Although metanephric adenofibroma is one of the rarest benign renal tumors, the clinical importance of correctly diagnosing it cannot be overemphasized because it can potentially be mistaken as Wilms' tumor. We describe the clinical, radiologic, and pathologic features of a case of metanephric adenofibroma and discuss its differential diagnosis. The neoplasm was composed of two discrete components: a major fibroblastic element and a minor immature epithelial element. The latter formed a small nodule beneath the renal capsule, which could barely be detected by magnetic resonance imaging. This subcapsular nodule, however, was slightly soft and tan and was distinctly different from the white, whorled cut surface of the main tumor. It was formed by closely packed small immature epithelial cells in a slightly edematous background, which was histologically identical to metanephric adenoma and closely resembled epithelial Wilms' tumor. Unlike Wilms' tumor, however, the epithelial cells were very bland with no mitoses. The main bulk of the tumor was formed by spindle fibroblastic cells that were cytologically similar to the spindle cells in congenital mesoblastic nephroma. The tumor, however, was well demarcated without the irregular infiltrating edges of congenital mesoblastic nephroma. In contrast to the randomly distributed epithelial element throughout the stromal component in previous reported cases of metanephric adenofibroma, our finding of the exceedingly small and discrete epithelial component expands the known histologic spectrum of the disease. In addition, the presence of such minute epithelial nodule underscores the importance of diligent pathologic examination and careful sampling of tissue for histologic examination.