Objective:To investigate the clinicopathological features, diagnosis, and prognosis of renal solitary fibrous tumor (SFT).Methods:Five cases of renal SFT with unequivocal diagnoses at the Affiliated Hospital of Qingdao University between January 2011 and July 2025 were subject to analyses of their clinical, morphological, immunophenotypic, and molecular characteristics, accompanied by a literature review.Results:Two males and three females aged between 45 and 62 years were included, all of whom presented with the discovery of a renal mass during routine physical examinations. Gross examination showed that the five tumors were all confined in the kidney. The tumors were nodular with maximum diameters ranging from 2.5 cm to 11.0 cm (mean, 5.8 cm). Upon cross-sectioning, they exhibited gray-white or gray-yellow cut surface. Histologically, the tumor cells exhibited oval or short spindle shapes in four cases, presenting with varying densities and arranged in short bundles, woven patterns, and irregular formation. Various amounts of coarse collagen and scattered staghorn blood-vessels were found in the stroma. In one case (case 5), the tumor cells were long spindle-shaped, densely organized in bundles, and interwoven, exhibiting inconspicuous boundaries, moderate nuclear atypia, and at least 4 mitotic figures per 10 high-power fields. Irregular patchy collagen deposition was particularly prominent at the edges of the tumor tissue. In two cases (cases 3 and 5), scattered and various amounts of renal tubules were observed in the tumor. Two cases (cases 4 and 5) demonstrated focal invasion of the renal parenchyma, although no necrosis was noted. Immunohistochemical staining showed that the tumor cells were diffusely and strongly positive for vimentin and STAT6 in all 5 cases, and positive for CD34. Bcl-2 positivity was present in 4 of the 5 cases. All cases were negative for CKpan, EMA, PAX8, HMB45, Melan A, SMA, and S-100 protein. The p53 status was wild type, and the Ki-67 index ranged from 1% to 8%. Next-generation sequencing was conducted on one case (case 4), revealing the NAB2 (exon 3)::STAT6 (exon 18) gene fusion. The 5 patients were followed up for 1 to 158 months (mean, 56 months), and all were alive with no recurrence or metastasis.Conclusions:SFT of the kidney are rare and morphologically similar to extrarenal SFT. Key morphological features include short spindle-shaped tumor cells arranged in bundles, interwoven patterns or irregularly, accompanied by staghorn blood-vessels and scattered coarse hyaline collagen fibers. SFT with epithelial inclusions may represent a relatively common histological subtype in the kidney. Immunohistochemical staining that demonstrates diffuse and strong positivity for STAT6 and CD34 is instrumental in diagnosing this tumor. The pathogenesis is linked to the centromeric inversion of chromosome 12q, resulting in the fusion of the NAB2 and STAT6 genes. Most of these tumors exhibit favorable prognosis.

Objective:To investigate the clinicopathological features, diagnosis, and prognosis of renal solitary fibrous tumor (SFT).Methods:Five cases of renal SFT with unequivocal diagnoses at the Affiliated Hospital of Qingdao University between January 2011 and July 2025 were subject to analyses of their clinical, morphological, immunophenotypic, and molecular characteristics, accompanied by a literature review.Results:Two males and three females aged between 45 and 62 years were included, all of whom presented with the discovery of a renal mass during routine physical examinations. Gross examination showed that the five tumors were all confined in the kidney. The tumors were nodular with maximum diameters ranging from 2.5 cm to 11.0 cm (mean, 5.8 cm). Upon cross-sectioning, they exhibited gray-white or gray-yellow cut surface. Histologically, the tumor cells exhibited oval or short spindle shapes in four cases, presenting with varying densities and arranged in short bundles, woven patterns, and irregular formation. Various amounts of coarse collagen and scattered staghorn blood-vessels were found in the stroma. In one case (case 5), the tumor cells were long spindle-shaped, densely organized in bundles, and interwoven, exhibiting inconspicuous boundaries, moderate nuclear atypia, and at least 4 mitotic figures per 10 high-power fields. Irregular patchy collagen deposition was particularly prominent at the edges of the tumor tissue. In two cases (cases 3 and 5), scattered and various amounts of renal tubules were observed in the tumor. Two cases (cases 4 and 5) demonstrated focal invasion of the renal parenchyma, although no necrosis was noted. Immunohistochemical staining showed that the tumor cells were diffusely and strongly positive for vimentin and STAT6 in all 5 cases, and positive for CD34. Bcl-2 positivity was present in 4 of the 5 cases. All cases were negative for CKpan, EMA, PAX8, HMB45, Melan A, SMA, and S-100 protein. The p53 status was wild type, and the Ki-67 index ranged from 1% to 8%. Next-generation sequencing was conducted on one case (case 4), revealing the NAB2 (exon 3)::STAT6 (exon 18) gene fusion. The 5 patients were followed up for 1 to 158 months (mean, 56 months), and all were alive with no recurrence or metastasis.Conclusions:SFT of the kidney are rare and morphologically similar to extrarenal SFT. Key morphological features include short spindle-shaped tumor cells arranged in bundles, interwoven patterns or irregularly, accompanied by staghorn blood-vessels and scattered coarse hyaline collagen fibers. SFT with epithelial inclusions may represent a relatively common histological subtype in the kidney. Immunohistochemical staining that demonstrates diffuse and strong positivity for STAT6 and CD34 is instrumental in diagnosing this tumor. The pathogenesis is linked to the centromeric inversion of chromosome 12q, resulting in the fusion of the NAB2 and STAT6 genes. Most of these tumors exhibit favorable prognosis.

Objective:To investigate the clinicopathological features and differential diagnosis of eosinophilic vacuolated tumor (EVT).Methods:Seven cases of EVT with characteristic morphology and unequivocal diagnosis from the Affiliated Hospital of Qingdao University (6 cases), Qingdao, China and the 971 Hospital of PLA Navy (1 case), Qingdao, China between January 2010 and December 2021 were subject to morphological and immunohistochemical analyses. Additionally, whole exome sequencing (WES) was performed in two cases. Twenty-two cases of renal oncocytoma (RO) and 17 cases of eosinophilic chromophobe renal cell carcinoma (eChRCC) diagnosed at the same time were used as controls.Results:Four males and three females with a mean age of 42 years (range: 29-61 years) were included in the study. The tumors were nodular and well-circumscribed, with sizes ranging from 1.5 to 4.5 cm. On cross-section, they appeared gray-red or gray-white, solid, and soft. Tumor cells were arranged in nests, solid sheets, and acinar or small vesicular structures. These cells exhibited eosinophilic cytoplasm with large, prominent clear vacuoles and round nuclei with prominent nucleoli. Perinuclear halos were focally present in four cases, while small tumor cells with sparse cytoplasm and hyperchromatic nuclei were seen in one case. No necrosis or mitosis was noted. Edematous stroma was detected in three cases. All tumors were positive for CD117 and Cathepsin K, but negative for vimentin and CK7. CK20 was positive in scattered individual cells, and Ki-67 positivity ranged from 1% to 4%. Point mutations in MTOR were identified in both patients who were subject to the molecular analysis. Statistical differences in the expression of Cathepsin K, CD10, S-100A1, and Cyclin D1 between EVT and RO ( P<0.05) were significant, so were the differences in the expression of Cathepsin K, CD10, CK7 and claudin 7 between EVT and eChRCC ( P<0.001). Seven patients were followed up for 4 to 96 months (mean, 50 months), with no recurrences or metastases. Conclusions:EVT is a rare renal tumor that shares morphological and immunophenotypic features with RO and eChRCC, and it is closely linked to the TSC/MTOR pathway. The presence of large prominent transparent vacuoles in eosinophilic cytoplasm along with conspicuous nucleoli is its key morphological characteristics. The use of combined immunohistochemical stains greatly aids in its diagnosis. Typically, the tumor exhibits indolent biological behaviors with a favorable prognosis.

Objective:To investigate the clinicopathological characteristics of eosionphilic Chromophobe renal cell carcinoma (eChRCC), and differences in morphology, immunophenotype and clinical prognosis betweeneChRCC, renal oncocytoma(RO) and classic Chromophobe renal cell carcinoma (cChRCC).Methods:The clinicopathologic data of 17 patients diagnosed as eChRCC from the Affiliated Hospital of Qingdao University (13 cases) and 971 Hospital of PLA Navy (4 cases) from October 2006 to February 2019 were collected. Immunohistochemical analysis was carried out to compare the immunophenotypes between 17 cases with ChRCC, 27 cases with RO and 30 cases with cChRCC.Resuls:Among the 17 patients, seven were males and ten were females, and the age ranged from 40 to 75 years (median 54 years). Clinically, 15 cases of 17 were found accidentally by physical examination. The tumor size ranged from 1.8 cm to 10.0 cm (average 5.7 cm) and the cut surface of 15 cases were solid, one case was solicl and cystic, and one was cystic. Most showed gray to red, and partially soft, gray to yellow appearances. Microscopically, most tumors presented solid growth pattern with vary number of alveolar structures (12 cases). Some were predominately characterized by cystic structure (3 cases), alveolar structure(1 case) and microcapsule structure (1 case). There were boundaries with varying degrees of clarity between tumor cells in 16 cases. The cytoplasm of tumor cells was eosinophilic and the nuclei were small round or irregular with focal perinuclear haloes in 14 cases. Large polygonal cells with light-stained cytoplasm appeared focally in 9 cases, and edematous areas with scarce tumor cells were found in 4 cases. Among 7 cases, 4 cases focally invaded peripheral renal parenchyma, 2 cases invaded adipose tissues outside the renal capsule, and 1 case presented invasion of renal sinus. Immunohistochemically, all cases were moderate to strong positive for EMA and claudin-7. CK7, CD117 and Ksp-cad were highly expressed with the expression rates of 12/17, 15/17, 14/17, respectively. Cyclin D1, AMACR, CD10, S100A1, and RCC were rarely expressed with the expression rates of 4/17, 3/17, 4/17, 1/17 and 1/17, respectively. On the contrary, all cases were negative for vimentin, CAⅨ, HMB45 and Melan A. The Ki-67 proliferation index of the 17 cases was 1%?5%. Follow-up data were available for all 17 patients from 7 to 154 months. Among them, 15 patients were alive without tumor recurrence or metastasis, one patient died of pulmonary metastasis after 31 months of surgery and one patient died of hepatic metastasis after 38 months of surgery.Conclusion:eChRCC has overlapping morphology and immunophenotype with RO. eChRCC is characterized by solid nest or alveolar structure, distinct border between tumor cells, perinuclear halos and lacking of interstitial looseness and edema. Scattered large polygonal cells with light-stained cytoplasm in tumor tissue play a significant role in the diagnosis of eChRCC. The positive expression of CK7, CD117, claudin-7 and Ksp-cad, and negative expression of cyclin D1, S100A1 are helpful to the diagnosis and differential diagnosis of eChRCC. The prognosis of eChRCC after complete surgical resection is excellent and few cases may have long-term metastasis. There is no significant difference in prognosis between eChRCC and cChRCC, but eChRCC shows better outcome than RO.

Objective: To investigate the clinicopathologic characteristics, molecular and genetic features, differential diagnoses and prognosis of fumarate hydratase-deficient renal cell carcinoma (FH-RCC). Methods: The immunohistochemical (IHC) expression of FH in 391 renal neoplasms in tissue chips collected from the Affiliated Hospital of Qingdao University and 971 Hospital of PLA Navy from January 2011 to December 2017 was evaluated. The clinicopathologic data of eight FH negative cases were collected.Polymerase chain reaction (PCR) and sequencing were used to detect the changes in FH gene in three cases. Interphase FISH with a dual color and break-apart probe was applied to detect the TFE3 gene alteration in the cases showing TFE3 protein expression. Results: Among the eight patients, seven were male and one was female, and age ranged from 28 to 50 years (mean 39 years). Tumor size ranged from 3.5 cm to 12.0 cm (mean 7.9 cm). Renal pelvis invasion was identified in six cases, and the tumor emboli in renal vein and inferior vena cava were found in four patients. The cut surface of most tumors was solid, colorful, grayish white or yellow with no clear border showing invasive growth pattern. Microscopically, the tumors showed different proportions of papillary, tubular cystic, cribriform and solid structures. The tumor cells were rounded or polygonal with eosinophilic or amphotropic cytoplasm, round or oval nuclei, and focal large and prominent nucleoli (WHO/ISUP grade 3-4). Two cases had sarcomatoid or rhabdoid components. Intravascular tumor emboli were found in five cases. IHC staining showed most tumors expressed PAX8(7/8), CK19(7/8), vimentin (6/8) and P504s(8/8). However, other immunomarkers including CK7, CD10, CD117, RCC, 34βE12, HMB45 and Melan A were all negative. Sequencing showed all three cases had FH gene mutations in exon 1. FISH revealed no TFE3 gene translocation or amplification in the two cases with TFE3 IHC expression. Follow-up data were available in seven patients with the follow-up period from 11 to 66 months. Among them, five patients died between 11 to 31 months after the surgery because of extensive distant metastases of the tumor to the lung, liver and lymph nodes. The other two patients were alive at the 36th and 66th month after the surgery. Conclusions Morphologically, FH-RCC overlaps with papillary RCC, collecting duct carcinoma and tubular-cystic RCC, showing a mixture of papillary, tubular cystic, cribriform or tubular papillary structures with at least focal large and prominent nucleoli. The negative expression of FH and the detection of FH gene mutation could facilitate the diagnosis of the tumor. FH-RCC is a high aggressive tumor, prone to metastasize, and is associated with poor prognosis. The timely diagnosis of FH-RCC could benefit the patients and their relatives as well.