Smooth muscle and adenoma-like renal tumor: a previously unreported variant of mixed epithelial stromal tumor or a distinctive renal neoplasm?

Smooth Muscle and Adenoma-Like Renal Tumor (SMART)- A Rare Biphasic Renal Tumor with a Review

Smooth muscle and adenoma-like renal tumor (SMART) is a biphasic tumor composed of cytologically bland stromal and epithelial components. It has many histopathological mimickers. A 57-year-old man presented with a left renal mass. The left radical nephrectomy showed a 13.5 cm tumor involving the entire kidney. The microscopic examination showed an unencapsulated, well-circumscribed biphasic tumor composed predominantly of intersecting bundles of smooth muscle, admixed with focal epithelial components arranged in cystic, tubular, tubulopapillary, nests, and cords. Both the components lacked nuclear atypia. Using immunohistochemistry, the spindle cells were positive for SMA and desmin, focally positive for CD10, and negative for ER, PR, and HMB45. The epithelial cells were positive for PAX8 and keratin 7 and negative for CD10. We report an additional example of SMART with a literature review. Knowledge about this recently described entity would lead to a better understanding of the clinicopathological features and histogenesis of this tumor.

Mixed epithelial and stromal tumours of the kidney with malignant transformation: a clinicopathological study of four cases

Mixed epithelial and stromal tumour of the kidney is a complex benign neoplasm in which malignancy rarely arises. In this study, we report four mixed epithelial and stromal tumours in which sarcoma or carcinoma developed. In the first, a multifocal adenocarcinoma arose and areas of transition from benign to malignant epithelium were observed. Oestrogen and progesterone receptors were diffusely present in the nuclei of the spindle cell stroma of the benign component. The second was a sarcoma in which benign epithelial elements were intermixed. Outside the renal parenchyma, clusters of small benign glands surrounded by oestrogen receptor-positive benign stroma were present, supporting the diagnosis of mixed epithelial and stromal tumour. Fluorescence in situ hybridisation for SYT-SSX translocation and immunohistochemical results, specifically TLE1 -ativity, argued against primary renal synovial sarcoma. The patient died 24 months after surgery. The third tumour consisted of small blue round cells, positive for epithelial membrane antigen, BCL2, CD99, and FLI1. Throughout the tumour, the presence of benign appearing branching tubules in fibromuscular stroma, reactive for smooth muscle actin, desmin and progesterone receptor, supported the diagnosis of mixed epithelial and stromal tumour in which a small round blue cell sarcoma with EWSR1 rearrangement arose. In the fourth tumour, adenocarcinoma with papillary architecture arose in a typical mixed epithelial and stromal tumour. In summary, we present four cases of mixed epithelial and stromal tumour with malignant transformation, two showing carcinomatous and the other two with sarcomatous transformation. Identification of typical benign looking elements and the absence of SYT-SSX translocation are helpful in recognition of this entity.

Thyroid-Like Follicular Renal Cell Carcinoma Arising Within Benign Mixed Epithelial and Stromal Tumor

Thyroid-like follicular renal cell carcinoma (TLF-RCC) is an extremely rare tumor with less than 40 published reports. These tumors are morphologically distinct with striking resemblance to thyroid follicular tumors, but immunohistochemically different due to lack of thyroglobulin and thyroid transcription factor 1 expression. TLF-RCCs arise in younger patients (mean age = 41 years) with female predominance and in all reported cases were solitary tumors without coexisting epithelial or mesenchymal kidney neoplasms. In this article, we report a case of a 42-year-old woman who presented with an incidental 4-cm solid and cystic left renal mass of the upper pole, which was resected. A detailed imaging assessment, pathologic findings, and immunohistochemical studies revealed a partially encapsulated TLF-RCC arising in a background of mixed epithelial and stromal tumor.

Mixed Epithelial and Stromal Tumor of the Kidney with Extension into Inferior Vena Cava: Case Report and Discussion of Adult Biphasic Cystic Renal Lesions and the Significance of Vascular Involvement

Mixed epithelial and stromal tumor (MEST) is a biphasic adult renal lesion composed of solid and cystic areas containing spindle cell stroma and epithelium that lines the tubules and cystic spaces. While most MEST lesions are benign, rare cases with malignant morphology and biology have been reported. We present a case of mixed epithelial and stromal tumor of the kidney (MEST) with extension into the inferior vena cava in a young adult male. We discuss the differential diagnosis of MEST in the context of other biphasic cystic renal lesions and the significance of vascular involvement in the setting of an otherwise benign tumor morphology.

Pediatric Cystic Nephroma Is Morphologically, Immunohistochemically, and Genetically Distinct From Adult Cystic Nephroma

The term cystic nephroma has traditionally been used to refer to 2 neoplasms, a lesion in adults that is now thought to be part of the spectrum of mixed epithelial stromal tumor (MEST) and a pediatric lesion that has been associated with mutations in the DICER1 gene. A direct detailed morphologic, immunohistochemical, and genetic comparison of these 2 lesions has not been performed. In this study, we compare the morphologic features, immunoreactivity for estrogen receptor and inhibin, and DICER1 genetic status of 12 adult cystic nephroma/MEST (median age 50.5 y, all females) and 7 pediatric cystic nephroma (median age 1.3 y, male:female=6:1). Both lesions (11 of 12 adult cases, 6 of 7 pediatric cases) frequently demonstrated subepithelial accentuation of stromal cellularity, though the increased cellularity frequently included inflammatory cells in the pediatric cases. All adult and pediatric cases labeled for estrogen receptor; however, whereas most (83%) of adult cases labeled for inhibin at least focally, no pediatric case labeled for inhibin. Most adult cases (58%) demonstrated wavy, ropy collagen in association with cellular stroma, whereas this was not found in pediatric cases. 86% of pediatric cases demonstrated DICER1 mutations, whereas only 1 of 10 adult cases demonstrated a DICER1 mutation. In summary, although cellular stroma and estrogen receptor immunoreactivity are commonly present in both adult and pediatric cystic nephroma, ropy collagen and inhibin immunoreactivity are far more common in adult cystic nephroma/MEST, whereas DICER1 mutations are far more prevalent in pediatric cystic nephroma. These results support the current World Health Organization Classification's separation of adult and pediatric cystic nephromas as distinct entities.

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.