Primary Renal Mesenchymal Neoplasms in Nephrectomy Specimens: A 16-Year Survey of Primary and Incidental Cases From a Single Institution

CD34-Negative Malignant Renal Solitary Fibrous Tumor: Case Report and Diagnostic Insights

Solitary fibrous tumors (SFTs) are rare fibroblastic neoplasms with diverse biological behaviors and widespread distribution. Primary renal SFTs are uncommon, and their malignant variants, especially those that are CD34 negative, are even rarer. This study presents a case of malignant renal SFT in a 57-year-old female, focusing on its immunomorphological features. On gross examination, the tumor's large size (11.5 cm) was remarkable. Microscopic analysis showed high cellularity, diffuse sheets of moderately pleomorphic ovoid cells, prominent staghorn vessels, tumor cell necrosis, and a high mitotic count. Immunohistochemistry revealed strong positivity for STAT6, vimentin, and Bcl-2 and, notably, negativity for CD34. The presence of the NAB2::STAT6 gene fusion was confirmed through fluorescence in situ hybridization. This case emphasizes the need to consider SFT in the differential diagnosis of unusual renal tumors, even when CD34 is negative. The infrequency, morphological diversity, and resemblance to other tumors make diagnosing renal SFTs challenging. Accurate identification and classification as benign or malignant are crucial for proper clinical management and prognosis.

A Contemporary Clinicopathologic Analysis of Primary Sarcomas of the Perinephric Soft Tissue and Hilar Vessels Including a Subset Secondarily Involving the Kidney

A variety of primary malignant mesenchymal neoplasms can arise from the perinephric soft tissue and hilar vessels and potentially involve the kidney, mimicking primary renal tumors. A search was made at our institution for patients that underwent radical nephrectomy with associated perinephric or hilar sarcomas from 2010 to 2021. Twenty-six patients were identified. Mean patient age was 60 years (range: 34-83 years), with 16 (62%) females and 10 (38%) males. The mean tumor size was 21.6 cm (range: 8.1-36.5 cm). Among the perinephric/retroperitoneal sarcomas, 14/20 (70%) were dedifferentiated liposarcoma, 4/20 (20%) were well-differentiated liposarcoma, and 2/20 (10%) were leiomyosarcoma. There were 4 grade 1 (20%; all well-differentiated liposarcoma), 9 grade 2 (45%), and 7 grade 3 (35%) tumors. All 6 sarcomas arising from the renal vein/inferior vena cava were leiomyosarcoma: grade 2 in 1 (17%), grade 3 in 4 (67%), and ungraded (due to neoadjuvant therapy effect) in 1 (17%) patient. Four of the 26 (15%) tumors involved the ipsilateral kidney. All 4 tumors were grade 3 sarcomas. On follow-up, 8/26 (31%) patients developed local recurrence and/or metastasis. The mean time for recurrence was 22 months (range: 7-48 months). Two patients progressed with metastasis to the lungs, both of which were grade 3 leiomyosarcoma, and appeared 11 months after the initial diagnosis. Our data suggest that while local recurrence is prevalent with most subtypes of perinephric sarcomas, high-grade leiomyosarcoma has a distinct proclivity for distant metastasis, with the lungs being the most common site.

Clinicopathologic and Immunohistochemical Characterization of Sarcomatoid Chromophobe Renal Cell Carcinoma: An Analysis of 22 Cases

Sarcomatoid differentiation in chromophobe renal cell carcinoma (ChRCC) is a rare finding and a significant predictor of worse outcomes. When the sarcomatoid component overgrows the conventional component or is the only component on a biopsy, the differential diagnoses encompass a variety of entities. Therefore, we reviewed 22 sarcomatoid ChRCCs and characterized the immunophenotype. Given that renal carcinomas with sarcomatoid features may benefit from immune checkpoint inhibitor-based therapy we also assessed the programmed death-ligand 1 (PD-L1) (28-8) expression. DOG1, CD117, cytokeratin 7, and PAX8 were negative in 100%, 88%, 63%, and 44% of the sarcomatoid components, respectively. GATA3 was expressed in 31% of the conventional components and in 50% of the sarcomatoid components. One conventional and 3 sarcomatoid components expressed PD-L1. Sarcomatoid ChRCCs have a high propensity for metastases and cancer progression. Distant metastatic disease was seen in 73% of the cases and median survival in this cohort was <1 year. The sarcomatoid portion had increased expression of PD-L1 and frequent loss of expression of multiple immunohistochemical markers associated with ChRCC. Half of the sarcomatoid ChRCC exhibited GATA3 expression, 3 of which did not express PAX8.