Letter to the Editor

Papillary renal cell carcinoma with prominent spindle cell stroma - tumor mimicking mixed epithelial and stromal tumor of the kidney: Clinicopathologic, morphologic, immunohistochemical and molecular genetic analysis of 6 cases

Papillary renal cell carcinoma (PRCC) is currently a well-studied type of RCC. In addition to PRCC type 1, there are a number of other subtypes and variants of PRCCs which have been reported. We describe a series of 6 PRCCs with papillary, micropapillary and/or tubulopapillary architecture and prominent spindle cell stroma, resembling stroma in mixed epithelial and stromal tumor of the kidney (MESTK) or sarcomatoid RCC. Clinicopathologic, morphologic, immunohistochemical and molecular features were analyzed. All patients were males with an age range of 44-98 years (mean 65.3, median 65.5 years). Tumor size ranged from 2.4-11.4 cm (mean 5.8, median 4.5 cm). Follow-up data were available for 4 patients, ranging from 3 to 96 months (mean 42.75, median 36 months). Epithelial cells were mostly cylindrical with eosinophilic cytoplasm, showing nuclear grade 2 and 3 (ISUP/WHO). In all cases, loose to compact prominent stroma composed of spindle cells, without malignant mesenchymal heterologous elements was detected. No atypical mitoses were found, while typical mitoses were rare in both epithelial and stromal components. Epithelial cells were positive for CK7, AMACR, and vimentin in all cases, while negative for TFE3, HMB45, desmin, CD34, and actin. The stroma was positive for vimentin, actin and focally for CD34, while negative for CK7, AMACR, TFE3, HMB45, and desmin. Estrogen and progesterone receptors were completely negative. FH and SDHB expression was retained in all analyzable cases. Proliferative index was barely detectable in stromal component and low in epithelial component, ranging 0 to 5% positive stained cells/high power field. Copy number variation was variable with no distinct pattern. No mutations in CDKN2A, BAP1, MET were detected. PRCC with MESTK-like features is a distinct variant of PRCC mimicking MESTK. Our findings add to the body of literature on ever expanding variants of PRCCs. Both epithelial and stromal components lacked true Müllerian features, which was also proven by immunohistochemistry.

Malignant Mixed Epithelial and Stromal Tumor of the Kidney With 2 Simultaneous Renal Carcinomas in a Male Patient: Case Report and Review of the Literature

The majority of mixed epithelial and stromal tumors (MEST) of the kidney are benign entities found in female patients. Malignant MEST of the kidney is an extremely rare entity that often behaves clinically similar to an undifferentiated sarcoma. We report a case of a malignant MEST with synchronous papillary and clear cell renal cell carcinomas (RCCs) in a 61-year-old Caucasian man who presented with an incidental finding of a left renal mass on workup for back pain. The patient underwent a left radical nephrectomy, with histopathology confirming a malignant MEST, intimately associated papillary RCC, and separate adjacent focus of clear cell RCC.

Paratesticular cystadenomas with ovarian stroma, metaplastic serous Müllerian epithelium, and male adnexal tumor of probable wolffian origin: A series of 5 hitherto poorly recognized testicular tumors

We present 5 paratesticular tumors, which manifested ovarian-type stroma and various serous müllerian epithelial structures including serous fallopian-like epithelium and proliferations closely mimicking cystic serous borderline tumors of the ovary. In addition, 3 of the tumors in our series revealed a solid epithelial component, which was morphologically and immunohistochemically similar to so called "female adnexal tumor of probable wolffian origin," which is a rare neoplasm described so far only in the female genital tract, retroperitoneum, and the pelvic cavity. In analogy with mixed epithelial and stromal tumors of the kidney, which are renal neoplasms producing ovarian-type stroma, we suggest to designate the above paratesticular tumors containing ovarian-type stroma as "mixed epithelial and stromal tumors of the paratestis with features of cystic serous borderline tumor" (cases 1 and 2) and "mixed epithelial and stromal tumors of the paratestis with male adnexal tumor of probable wolffian origin" (cases 3-5).

Cystic renal tumors: new entities and novel concepts

Cystic renal neoplasms and renal epithelial stromal tumors are diagnostically challenging and represent some novel tumor entities. In this article, clinical and pathologic features of established and novel entities are discussed. Predominantly cystic renal tumors include cystic nephroma/mixed epithelial and stromal tumor, synovial sarcoma, and multilocular cystic renal cell carcinoma. These entities are own tumor entities of the 2004 WHO classification of renal tumors. Tubulocystic carcinoma and acquired cystic disease-associated renal cell carcinoma are neoplasms with an intrinsically cystic growth pattern. Both tumor types should be included in a future WHO classification as novel entities owing to their characteristic features. Cysts and clear cell renal cell carcinoma frequently coexist within the kidneys of patients with von Hippel-Lindau disease. Sporadic clear cell renal cell carcinomas often contain cysts, usually as a minor component. Some clear cell renal cell carcinomas have prominent cysts, and multilocular cystic renal cell carcinoma is composed almost exclusively of cysts. Recent molecular findings suggest that clear cell renal cancer may develop through cyst-dependent and cyst-independent molecular pathways.

Mixed epithelial and stromal tumour of the kidney: imaging features

OBJECTIVE

To describe the features on ultrasonography (US), computed tomography (CT) and magnetic resonance imaging (MRI) of mixed epithelial and stromal tumours of the kidney.

PATIENTS AND METHODS

Five women with renal mixed epithelial and stromal tumours (mean age 55.6 years, range 49-59) who had preoperative imaging were retrospectively analysed. Three ultrasonograms, five contrast-enhanced CT scans, and one contrast-enhanced MRI examination were available for review. Specific imaging features analysed included lesion size, location, enhancement and cystic composition. The presence of calcification, septation, nodularity and a capsule were also evaluated.

RESULTS

All mixed epithelial and stromal tumours appeared as well-marginated, multi-septate cystic masses with a nodular component. All lesions were classified as Bosniak category III (three) or IV (two). The presence of calcification (four) or a capsule (three) was variable. Two tumours invaginated into the renal pelvis with no invasion.

CONCLUSION

Mixed epithelial and stromal tumours of the kidney have a diverse radiographic appearance, indistinguishable from multilocular cystic nephroma and cystic renal cell carcinoma.

Renal angiomyoadenomatous tumor: morphologic, immunohistochemical, and molecular genetic study of a distinct entity

We present a series of a distinct tumorous entity named renal angiomyoadenomatous tumor (RAT). Five cases were retrieved from the consultation files of the authors. Histologic and immunohistochemical features were evaluated. Sequencing analysis of coding region of the VHL gene was carried out in all cases. The tumors were composed of admixture of an epithelial clear cell component and prominent leiomyomatous stroma. Epithelial cells formed adenomatous tubular formations endowed with blister-like apical snouts. All tubular/glandular structures were lined by a fine capillary network. The epithelial component was positive for epithelial membrane antigen, CK7, CK20, AE1-AE3, CAM5.2, and vimentin in all cases. In all analyzed samples, no mutation of the VHL gene was found. RAT is a distinct morphologic entity, being different morphologically, immunohistochemically, and genetically from all renal tumors including conventional clear cell carcinoma and mixed epithelial and stromal tumor of kidney.

A case report of a renal mixed epithelial and stromal tumor in a heterozygous S1P2 receptor deficient mouse

We report a case of mixed epithelial and stromal tumor of the kidney (MESTK) in a 32-week-old heterozygous sphingosine 1-phosphate-2 (S1P2) receptor deficient female mouse. A white solid mass replacing the left kidney was observed at the left retroperitoneal wall. Histologically, the tumor mass consisted of dimorphic cellular components of epithelial and stromal cells. Epithelial cells formed various sized irregular-shaped tubular structures resembling renal tubules surrounded by stromal cells. Immunohistochemically, epithelial cells were positive for cytokeratin, while stromal cells showed positive immunoreactivity with alpha-smooth muscle actin as well as vimentin. Based on the morphological and immunohistochemical findings, this tumor was diagnosed as a MESTK.

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.

Large mixed epithelial and stromal tumor of the kidney masquerading as metastatic renal cell carcinoma

We report the case of a 39-year-old woman with a large right renal mass 20 cm in size with heterogeneous solid and cystic components as well as concurrent liver lesions suspicious for metastatic renal cell carcinoma. Surgical extirpation of the renal mass and liver lesions was performed laparoscopically with the pathological analysis revealing a rare renal neoplasm--mixed epithelial and stromal tumor of the kidney--and adenomas of the liver.

Cystic nephroma and mixed epithelial and stromal tumour of the kidney: opposite ends of the spectrum of the same entity?

OBJECTIVES

The term "renal epithelial and stromal tumour" (REST) was proposed recently to encompass the spectrum of findings observed in cystic nephroma (CN) and mixed epithelial and stromal tumour (MEST) of the kidney. Our aim was to review the broad spectrum of usual and unusual clinical and morphologic findings observed in CN and MEST.

METHODS

Based on Medline database searches, all aspects of CN and MEST were assessed.

RESULTS

CN and MEST have a remarkable similarity 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-like stroma, smaller cysts, and stromal luteinisation in MEST, and large cysts, thin septa, and low stromal-to-epithelial ratio in CN. The stromal component in both lesions expresses estrogen and progesterone receptors. Rare and unusual morphologic features, such as endometrioid, cervical, and intestinal differentiation, and luteinised ovarian-like stroma, have been described in MEST. The epithelial element occasionally shows estrogen and progesterone receptors. Rare aggressive behaviour has been reported for both neoplasms.

CONCLUSIONS

Considerable overlap is apparent between the two lesions, which suggests that they may represent opposite ends of the spectrum of the same process. Even though an aggressive behaviour has been reported in very few cases, in general both neoplasms are considered benign and surgical excision is curative.

Mixed epithelial and stromal tumor of the kidney in a puerperal woman

Puerperal pyrexia is still rampant, especially in third world countries, and is usually due to puerperal sepsis, urinary tract infections, upper respiratory infection, and breast infection. Rarely, in third world countries like India, it may be due to tuberculosis, malaria, typhoid, and so on, which are also rampant in the general population. Mixed epithelial and stromal tumor of the kidney (MESTK) is a recently recognized subset of renal tumors composed mainly of smooth muscle cells in which epithelial structures are embedded. It usually occurs in middle aged and older women. In the present case report, a 36-year-old woman presented with puerperal pyrexia, possibly due to tuberculosis and with an incidental mixed epithelial and stromal tumor of the kidney causing complex ascitis and fever, which required nephrectomy that was followed by full recovery. This case report highlights the importance of keeping MESTK in mind even in younger women with asymptomatic renal mass. It also highlights the importance of keeping renal tumors in mind as a possibility and to perform proper investigations for adequate treatment and recovery.

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.

Cystic nephroma (multilocular cyst) and mixed epithelial and stromal tumor of the kidney: a spectrum of the same entity?

The recently described mixed epithelial and stromal tumor (MEST) of the kidney and adult cystic nephroma (CN) (multilocular cyst) are rare benign cystic renal neoplasms that are composed of epithelial and stromal elements. Consensus criteria for distinguishing these entities have not been well established. Our objective in this study was to evaluate cases of CN and MEST to define the morphological, immunophenotypic, and clinical features of these two entities. Eleven cases from the files of a single institution diagnosed from 1996 to the present as either CN or MEST were reviewed. Architecturally, all lesions were composed of multiple noncommunicating cysts lined by a single layer of epithelial cells. All cases had areas with increased stromal cellularity and 8 cases had ovarian-like stroma present at least focally within the tumor. No stromal or epithelial cell atypia, blastemal elements, or increased mitotic activity was appreciated. The immunoprofile was also similar in the 7 cases stained and included epithelial reactivity with keratin and CAM 5.2 and stromal reactivity with estrogen receptor, progesterone receptor, smooth muscle actin, WT-1, vimentin, and focal desmin. All cases have acted in a benign fashion with no history of recurrence or metastasis. We propose that CN and MEST of the kidney represent a spectrum of the same entity. If the diagnosis of CN is limited to cases that are comprised entirely of thin fibrous-walled cysts, all 11 of our cases would be classified as MEST.

Renal cystic diseases: a review

This review aims to assist in the categorization of inherited, developmental, and acquired cystic disease of the kidney as well as to provide a pertinent, up-to-date bibliography. The conditions included are autosomal-dominant polycystic kidney disease, autosomal-recessive polycystic kidney disease, unilateral renal cystic disease (localized cystic disease), renal simple cysts, multicystic dysplastic kidney, pluricystic kidney of the multiple malformation syndromes, juvenile nephronophthisis and medullary cystic disease, medullary sponge kidney, primary glomerulocystic kidney disease, and glomerulocystic kidney associated with several systemic disorders mainly of genetic or chromosomal etiology, cystic kidney in tuberous sclerosis, and in von Hippel-Lindau syndrome, cystic nephroma, cystic variant of congenital mesoblastic nephroma, mixed epithelial stromal tumor of the kidney, renal lymphangioma, pyelocalyceal cyst, peripylic cyst and perinephric pseudocyst, acquired renal cystic disease of long-term dialysis, and cystic renal cell carcinoma and sarcoma. Whereas the gross and histologic appearance of some of these conditions may be diagnostic, clinical and sometimes molecular studies may be necessary to define other types.

Extensively Cystic Renal Neoplasms in Adults (Bosniak Classification II or III) – Possible “Common” Histological Diagnoses: Multilocular Cystic Renal Cell Carcinoma, Cystic Nephroma, and Mixed Epithelial and Stromal Tumor of the Kidney

OBJECTIVE(S)

To give an algorithm for resolution of extensively cystic renal neoplasms, preoperatively classified in the Bosniak classification as a category II and III.

METHODS

From 1991 to 6/2004, 701 patients with 727 renal tumours were surgically treated at our hospital. Extensively cystic tumours were found in 10 cases. Extensively cystic tumours were defined as multicystic tumours without any solid nodules visible neither on CT, nor grossly in the specimen at operation (the Bosniak classification type II or III).

RESULTS

Seven multilocular cystic renal cell carcinomas, three mixed epithelial and stromal tumour of the kidney and one cystic nephroma were diagnosed on histology.

CONCLUSION(S)

Extensively cystic renal tumours classified as the Bosniak type II or III correspond histologically to the entities mentioned above (multilocular cystic renal cell carcinoma, cystic nephroma, mixed epithelial and stromal tumour of the kidney). These entities cannot be distinguished one from another on preoperative imaging studies. A preoperative biopsy and intra-operative frozen-section analysis do not lead to a correct diagnosis in many cases. Fortunately, the operative strategy is the same for all these tumours. In such cases, the nephron sparing surgery is indicated, whenever technically feasible, as almost all extensively cystic renal tumours have a good prognosis.

[Tumors of the kidneys: new entities]

Since 1998 new entities have surfaced in renal tumor classification and have been included in the WHO 2004 classification. In this article, we will discuss the following entities: multilocular clear cell renal carcinoma, Xp11 translocation carcinoma, low grade mucinous tubular carcinoma, epithelioid angiomyolipoma, benign mixed epithelial and stromal tumor. We will investigate new concepts of hybrid oncocytoma and chromophobe renal cell carcinoma and the syndrome of Birt-Hogg-Dube which is associated to kidney tumors. At least, we will touch on new elements in the Bellini carcinoma definition.

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.