Differential expression of cathepsin K in neoplasms harboring TFE3 gene fusions

Unlocking diagnostic potential: A retrospective analysis of GPNMB immunohistochemistry in nearly 1000 surgical pathology specimens

Glycoprotein non-metastatic melanoma protein B (GPNMB) is a lysosomal transmembrane protein regulated by the TSC/mTOR-TFE pathway and has been proposed as a diagnostic immunohistochemical (IHC) marker for tumors associated with TSC/mTOR-TFE pathway alterations. However, its diagnostic performance in routine surgical pathology has not been systematically evaluated on a large scale. We retrospectively reviewed 934 cases from the Johns Hopkins pathology archives (2021-2025) in which GPNMB IHC was performed. Diagnoses were categorized into TSC/mTOR-TFE-related, non-TSC/mTOR/TFE-related, or undefined molecular groups. Correlation with fluorescence in situ hybridization (FISH) results and histologic features was performed to assess diagnostic utility. GPNMB was diffusely positive in 94.8 % (218/230) of TSC/mTOR-TFE-related neoplasms, including renal cell carcinomas with TFE3/TFEB rearrangements, perivascular epithelioid cell tumors (PECOMA/AML), and other related entities. In contrast, 83.3 % of non-TSC/mTOR-TFE-related tumors were negative for GPNMB. Discordant cases were seen in both groups, likely reflecting molecular heterogeneity, limitations of FISH, or the complex regulation of GPNMB expression. GPNMB outperformed cathepsin K in sensitivity in FISH-confirmed cases with TFE3 or TFEB alterations. Patchy or equivocal staining required careful histologic and ancillary correlation for interpretation. GPNMB IHC is a valuable ancillary tool in diagnosing TSC/mTOR-TFE-related neoplasms, particularly in renal and mesenchymal tumors. While not perfectly specific or sensitive, it offers a rapid and cost-effective alternative to molecular testing and can guide further diagnostic workup. Positive GPNMB staining in tumors without known TSC/mTOR-TFE alterations may suggest secondary pathway involvement, warranting additional molecular studies.

Primary Uterine Alveolar Soft Part Sarcoma in a Postmenopausal Woman: Histopathologic and Immunohistochemical Characteristics of a Rare Case

BACKGROUND

Primary uterine alveolar soft part sarcoma (ASPS) is a rare, indolent mesenchymal malignancy with less than 40 patients documented in the literature.

CASE

We report an example of ASPS in a 61-year-old postmenopausal woman. Macroscopically, the uterus showed multiple nodular masses. Microscopic examination revealed tumor arranged in nests and alveolar pattern. The tumor cells were moderately to markedly pleomorphic, epithelioid to polygonal, with eccentrically placed nuclei, vesicular chromatin, prominent macro-nucleoli, and moderate to abundant eosinophilic cytoplasm. PAS-positive and diastase-resistant intracytoplasmic crystals were also seen in some tumor cells. On immunohistochemistry, the tumor cells showed diffuse positivity for vimentin and nuclear positivity for TFE3, a surrogate marker for ASPS. These were negative for SMA, desmin, CD10, h-caldesmon, cyclin D1, EMA, Melan A, and CD34. SMARCB1 expression was retained. Based on the histopathology and IHC, a final diagnosis of uterine ASPS was rendered.

CONCLUSIONS

Knowledge of the characteristic histopathologic and immunohistochemical features can help accurately diagnose such rare tumors. Knowledge of the characteristic histopathologic and immunohistochemical features can help accurately diagnose such rare sarcoma in an uncommon site with an unusual age.

Renal epithelioid angiomyolipomas overexpress TFE3 and the TFE3-regulated gene TRIM63 in the absence of TFE3 rearrangement

Angiomyolipoma (AML) is a neoplasm within the perivascular epithelioid cell tumor family that occurs somewhat frequently in the kidney. Most are indolent and discovered incidentally, with rare tumors demonstrating malignant clinical behavior. A small subset of renal AMLs with epithelioid features are associated with aggressive behavior, and may demonstrate morphologic overlap with renal cell carcinomas (e.g., clear cell renal cell carcinoma (RCC), TFE3-rearranged RCC). Prior studies of spindle cell and epithelioid AMLs have identified rare examples with underlying TFE3 gene fusions. TFE3 protein expression (demonstrated by immunohistochemistry) with no evidence of concurrent TFE3 rearrangements has been reported previously in 4/24 AMLs (17%) (Argani et al. Am J Surg Pathol 34:1395-1406, 2010). Currently, the relationship between TFE3 protein expression, TFE3 fusions, and expression of TFE3-mediated genes remains incompletely understood in renal epithelioid AMLs. We sought to explore these relationships using TFE3 break-apart fluorescence in situ hybridization (FISH) and TRIM63 RNA in situ hybridization (ISH) on epithelioid AMLs with moderate to strong TFE3 expression by immunohistochemistry. RNA sequencing (fusion panel) was performed on two cases with negative FISH results to assess for FISH-cryptic gene fusions. The series comprised five epithelioid AMLs from four patients (three women, one man) aged 13 to 76 years. All were considered positive for TFE3 by immunohistochemistry (2 + /3 + expression). TRIM63 ISH was performed on four specimens from three patients, yielding positive results in 3/3 tumors (100%) that were successfully analyzed. TFE3 break-apart FISH was performed on all samples, demonstrating a TFE3 rearrangement in only 1/4 tumors (25%). RNA sequencing demonstrated the absence of productive TFE3 gene fusions in three tumors with negative break-apart TFE3 FISH results. This study demonstrates that renal epithelioid AMLs overexpress TFE3 and TFE3-mediated genes (TRIM63) even in the absence of TFE3 rearrangements. This finding could be explained by functional upregulation of TFE3 secondary to activation of the mammalian target of rapamycin complex 1 (mTORC1). Expression of TFE3 and TRIM63 in this tumor type represents a potential pitfall, given the morphologic and immunophenotypic overlap between epithelioid AML and TFE3-altered renal cell carcinoma.

Incidental Detection of TFEB-Amplified Renal Cell Carcinoma by Colocated Gene Amplification of CCND3 (6p21): A Case Report and Review of the Literature

TFEB-amplified renal cell carcinoma (RCC), which belongs to the MITF family of RCC, is characterized by genomic amplification at the 6p21.1 locus where the TFEB gene is located. The vascular endothelial growth factor A and cyclin D3 genes are also located at this same locus. When tumors lack classic morphologic features, they may be classified as "RCC not otherwise specified (NOS)." However, it is increasingly important to accurately diagnose the RCC subtype to define the patient's individual prognosis and select the subsequent therapeutic modalities, which now include targeted agents. Therefore, knowledge of the diagnostic features of TFEB-altered RCCs, such as t(6;11) RCCs and TFEB-amplified RCCs, is critical for identifying these tumors. Herein, we present an interesting case of TFEB-amplified RCC that was initially diagnosed as RCC NOS on biopsy of a renal tumor in a community practice setting with available molecular findings demonstrating CCND3 amplification. The genetic abnormality was "accidentally" detected due to the amplification of the colocated CCND3 gene at the 6p21 locus of the TFEB gene on a limited genetic sequencing panel. This case highlights the importance of molecular tests in accurately diagnosing RCC and carefully interpreting molecular findings in the context of histomorphologic features.

MiT family translocation-associated renal cell carcinoma: A report of two cases in children

ABSTRACT

Renal cell carcinoma is uncommon in children and must be distinguished from the more common Wilms' tumor. Here, we present two cases of renal cell carcinoma in children both of whom presented with hematuria. Accurate diagnosis is essential in order to differentiate it from epithelial predominant Wilms' tumor which has vastly different prognosis and treatment. Immunohistochemistry for TFE3 is useful in establishing the diagnosis.

Glycoprotein Nonmetastatic Melanoma Protein B (GPNMB) Immunohistochemistry Can Be a Useful Ancillary Tool to Identify Perivascular Epithelioid Cell Tumor

Perivascular epithelioid cell tumors (PEComas) are rare mesenchymal tumors that express smooth muscle and melanocytic makers. Diagnosis of PEComas can be challenging due to focal or lost expression of traditional immunohistochemical markers, limited availability of molecular testing, and morphological overlap with much more common smooth muscle tumors. This study evaluates the use of glycoprotein nonmetastatic melanoma protein B (GPNMB) immunohistochemical staining as a surrogate marker for TSC1/2/MTOR alteration or TFE3 rearrangement to differentiate PEComas from other mesenchymal tumors. Cathepsin K was also assessed for comparison. A total of 399 tumors, including PEComas, alveolar soft part sarcomas, and other histologic PEComa mimics, were analyzed using GPNMB and cathepsin K immunohistochemistry. GPNMB expression was seen in all PEComas and alveolar soft part sarcomas with the majority showing diffuse and moderate-to-strong labeling, whereas other sarcomas were negative or showed focal labeling. When a cutoff of diffuse and at least moderate staining was used, GPNMB demonstrated 95% sensitivity and 97% specificity in distinguishing PEComas from leiomyosarcoma, well-differentiated/dedifferentiated liposarcomas, and undifferentiated pleomorphic sarcomas. Cathepsin K with a cutoff of any labeling had lower sensitivity (78%) and similar specificity (94%) to GPNMB. This study highlights GPNMB as a highly sensitive marker for PEComas and suggests its potential use as an ancillary tool within a panel of markers for accurate classification of these tumors.

Evaluation of TRIM63 RNA in situ hybridization (RNA-ISH) as a potential biomarker for alveolar soft-part sarcoma (ASPS)

Alveolar soft-part sarcoma (ASPS) is a rare soft tissue tumor with a broad morphologic differential diagnosis. While histology and immunohistochemistry can be suggestive, diagnosis often requires exclusion of other entities followed by confirmatory molecular analysis for its characteristic ASPSCR1-TFE3 fusion. Current stain-based biomarkers (such as immunohistochemistry for cathepsin K and TFE3) show relatively high sensitivity but may lack specificity, often showing staining in multiple other entities under diagnostic consideration. Given the discovery of RNA in situ hybridization (RNA-ISH) for TRIM63 as a sensitive and specific marker of MiTF-family aberration renal cell carcinomas, we sought to evaluate its utility in the workup of ASPS. TRIM63 RNA-ISH demonstrated high levels (H-score greater than 200) of expression in 19/20 (95%) cases of ASPS (average H-score 330) and was weak or negative in cases of paraganglioma, clear cell sarcoma, rhabdomyosarcoma, malignant epithelioid hemangioendothelioma, as well as hepatocellular and adrenal cortical carcinomas. Staining was also identified in tumors with known subsets characterized by TFE3 alterations such as perivascular epithelioid cell neoplasm (PEComa, average H-score 228), while tumors known to exhibit overexpression of TFE3 protein without cytogenetic alterations, such as melanoma and granular cell tumor, generally showed less TRIM63 ISH staining (average H-scores 147 and 96, respectively). Quantitative assessment of TRIM63 staining by RNA-ISH is potentially a helpful biomarker for tumors with molecular TFE3 alterations such as ASPS.

"Oncocytoid Renal Cell Carcinomas After Neuroblastoma" Represent TSC -mutated Eosinophilic Solid and Cystic Renal Cell Carcinomas : Association With Prior Childhood Malignancy and Multifocality With Therapeutic Implications

The concept of oncocytoid renal cell carcinoma in patients who have survived neuroblastoma as a distinct biologic entity has been controversial since its original description in 1999. This is in part because similar oncocytoid renal cell carcinomas have been described in association with other pediatric cancers, and also because other renal cell carcinoma subtypes (such as MiT family translocation renal cell carcinoma) have been described in children who have survived neuroblastoma. We identified an index case of a child who survived medulloblastoma and developed multifocal bilateral oncocytoid renal cell carcinomas with morphology and immunophenotype compatible with eosinophilic solid and cystic renal cell carcinoma (ESC RCC) and demonstrated that both neoplasms harbored distinctive mutations in the TSC1/TSC2 genes. Remarkably, the child's remaining bilateral multifocal renal neoplasms completely responded to MTOR inhibitor therapy without need for further surgery. To confirm our hypothesis that oncocytoid renal cell carcinomas after childhood cancer represent ESC RCC, we obtained formalin-fixed paraffin-embedded tissue blocks from 2 previously published cases of oncocytoid renal cell carcinoma after neuroblastoma, confirmed that the morphology and immunophenotype was consistent with ESC RCC, and demonstrated that both cases harbored somatic TSC gene mutations. Both expressed markers previously associated with neoplasms harboring TSC gene mutations, glycoprotein nonmetastatic B, and cathepsin K. Of note, one of these patients had 2 ESC RCC which harbored distinctive TSC2 mutations, while the background kidney of the other patient had multiple small cysts lined by similar oncocytoid cells which showed loss of TSC2 protein. We then reviewed 3 of 4 cases from the original 1999 report of oncocytoid renal cell carcinomas after neuroblastoma, found that all 3 demonstrated morphology (including basophilic cytoplasmic stippling) that is characteristic of ESC RCC, showed that all 3 overexpressed glycoprotein nonmetastatic B, and showed that both cases with adequate material demonstrated loss of TSC2 protein and expressed cytokeratin 20 and cathepsin K by immunohistochemistry. In summary, "oncocytoid renal cell carcinomas after neuroblastoma" represent ESC RCC which are often multifocal in patients who have survived childhood cancer, likely representing an incompletely characterized tumor predisposition syndrome. MTOR-targeted therapy represents an effective therapeutic option for such patients to preserve functional nephrons.

Prediction and therapeutic targeting of the tumor microenvironment-associated gene CTSK in gastric cancer

BACKGROUND

Cathepsin-K (CTSK) is overexpressed in Gastric cancer (GC) and the mechanism of its overexpression in GC is still unclear. The present work found CTSK as a potential predictive biomarker and immunotherapeutic target for GC based on the tumor microenvironment (TME).

METHODS

From public databases, gene expression profiles and clinical data of GC were downloaded to analyze the distribution of stromal and immune cells and tumor abundance in TME. Differentially expressed genes (DEGs) associated with TME were obtained by differential analysis, followed by cross-screening to obtain CTSK as a gene associated with TME. Next, a series of methods and tools were employed to explore the relationships between clinicopathological features of GC and CTSK expression as well as prognosis, tumor immune microenvironment, immune checkpoints and drug sensitivity. And GSEA was used to investigate the potential role of CTSK in the tumor microenvironment of GC.

RESULTS

From the dataset, we obtained a total of 656 DEGs associated with TME and the stromal component of TME was found to be closely involved in GC prognosis. CTSK was cross-screened as the key gene associated with TME by the PPI network and univariate Cox regression analysis. Pan-cancer analysis revealed significant high expression of CTSK in a variety of cancers. Subsequently, we hypothesized that high-expressed CTSK was closely correlated with poor prognosis and lymph node metastasis of tumors, and that CTSK, a GC TME-related gene, was largely involved in a range of biological behaviors of tumors, with a significant correlation between several immune cells.

CONCLUSION

CTSK was validated as a potential prognostic biomarker related to TME of GC and could be a promising next-generation immunotherapeutic target for GC.

Unravelling the mysteries of Xp11.2 translocation-associated renal cell carcinoma: A case report with a review of the literature

Cytomorphologic and immunocytochemical features of TFE3 translocation-associated renal cell carcinoma.

MED15::TFE3 Renal Cell Carcinomas: Report of Two New Cases and Review of the Literature Confirming Nearly Universal Multilocular Cystic Morphology

We report two novel cases of Xp11 translocation renal cell carcinomas with the MED15::TFE3 gene fusion in adult females aged 40 and 74 years. Both cases were extensively cystic and contained only minimal clear cells lining cysts and within septal walls, raising the differential diagnosis of multilocular cystic renal neoplasm of low malignant potential. By immunohistochemistry, both neoplasms labeled for PAX8, TFE3, cathepsin K and Melan A but not for HMB45. On review of the published literature and the two cases reported herein, over 90% of MED15::TFE3 renal cell carcinomas (RCCs) have been described as cystic. The correlation of the MED15::TFE3 fusion with extensively cystic morphology represents the strongest association of TFE3 fusion partner with clinicopathological features among TFE3-rearranged RCC reported to date.

TFE3 gene rearrangement and protein expression contribute to a poor prognosis of renal cell carcinoma

Background

TFE3-rearranged renal cell carcinoma (TFE3-rearranged RCC) is a type of kidney cancer with a low incidence, with no consensus about whether it has a worse prognosis than clear cell renal cell carcinoma (ccRCC). This study attempted to elucidate the impact of TFE3-rearranged RCC by analyzing its clinical features and prognosis.

Methods

Patients treated in Sun Yat-sen Memorial Hospital (SYSMH) who were suspected to be diagnosed with TFE3-rearranged RCC were divided into two groups, TFE3-rearranged RCC and ccRCC with positive TFE3 protein expression on immunohistochemistry [TFE3(+) ccRCC], by dual-color, break-apart fluorescence in situ hybridization (FISH). After balancing the baseline characteristics with TFE3(+) ccRCC using the propensity score matching (PSM) method in a ratio of 2, we selected patients diagnosed with ccRCC with negative TFE3 protein expression on immunohistochemistry [TFE3(-) ccRCC]. The impact of TFE3 gene rearrangement and protein expression on renal cell carcinoma was determined by feature comparison with a nonparametric test and survival analysis with the Kaplan‒Meier method.

Results

Among 37 patients suspected of having TFE3-rearranged RCC, 13 patients were diagnosed with TFE3-rearranged RCC, and 24 patients had TFE3(+) ccRCC. The recurrence and new metastasis of TFE3-rearranged RCC was relatively common, even if the tumor stage was early at the first diagnosis. Through feature comparison and survival analysis, we found that TFE3-rearranged RCC was quite similar to TFE3(+) ccRCC. Compared with TFE3(-) ccRCC, TFE3(+) ccRCC tended to have a larger tumor diameter (P = 0.011), higher neutrophil/lymphocyte ratio (NLR) (P = 0.017) and metastatic potential (P = 0.022), and worse overall survival (OS) (P = 0.043) and PFS (P = 0.016). The survival analysis showed that TFE3-rearranged RCC had a worse PFS than ccRCC (P = 0.002), and TFE3(+) RCC had a worse PFS than TFE3(-) RCC (P = 0.001). According to the stratification system based on the combination of TFE3 and lymphovascular invasion (LVI), we further found that the prognosis from good to poor was TFE3(-) LVI(-), TFE3(+) LVI(-), TFE3(+) LVI(+) and TFE3(-) LVI(+), with statistically significant differences in both OS (P = 0.001) and PFS (P < 0.001). In addition, we also reported two cases with poor prognosis, of which one was TFE3-rearranged RCC and the other was TFE3(+) ccRCC.

Conclusions

This is a novel finding that both FISH confirmed TFE3 gene rearrangement-mediated TFE3-rearranged RCC and IHC confirmed positive TFE3 protein expression [TFE3(+)] contribute to a poor prognosis in RCC, suggesting more active treatment and careful follow-up for TFE3(+) RCC patients. The combination of TFE3 and LVI may be a new risk stratification system for RCC.

The Recent Advances in Molecular Diagnosis of Soft Tissue Tumors

Soft tissue tumors are rare mesenchymal tumors with divergent differentiation. The diagnosis of soft tissue tumors is challenging for pathologists owing to the diversity of tumor types and histological overlap among the tumor entities. Present-day understanding of the molecular pathogenesis of soft tissue tumors has rapidly increased with the development of molecular genetic techniques (e.g., next-generation sequencing). Additionally, immunohistochemical markers that serve as surrogate markers for recurrent translocations in soft tissue tumors have been developed. This review aims to provide an update on recently described molecular findings and relevant novel immunohistochemical markers in selected soft tissue tumors.

TFE3-immunopositive papillary renal cell carcinoma: A clinicopathological, immunohistochemical, and genetic study

It is possible that PRCCs may still contain a variety of unknown histologic subtypes. Some PRCCs express high expression of TFE3 protein without TFE3 gene rearrangement, but no reports have investigated the significance of this. Here we attempted to examine clinicopathological and molecular significance of the TFE3-immunopositive PRCC. We reviewed the histology and immunohistochemistry in 58 PRCCs. TFE3 immunoexpression was recognized in 7 cases. Because TFE3 immunostaining shows false-positive, to ensure the integrity of TFE3 immunostaining, the immunostaining was performed under strict control of internal controls and western blotting was performed on 2 positive cases and 5 negative cases, and differences in protein expression between two groups were confirmed. Significant immunohistochemical expressions of autophagy/lysosome proteins were observed in TFE3-positive group. No TFE3 gene arrangement was detected in all positive cases by fluorescence in situ hybridization. Whole-exome sequencing was performed on 6 TFE3-positive and 2 TFE3-negative cases. Gain of chromosome 7 was found in five of 6 TFE3-positive cases (83%). TFE3-positive group was correlated significantly with higher pTstage, cNstage, WHO/ISUP nuclear grade, and decreased OS. TFE3-immunopositive PRCC group had a poorer prognosis than TFE3-negative PRCC group and showed correlation with expressions of autophagy/lysosome proteins, suggesting that enhancement of autophagy/lysosome function drives an environment of energy metabolism that is favorable for cancer. It is necessary to recognize that there is TFE3-immunopositive group without TFE3 gene rearrangement within PRCC. Because of its aggressive biological behaviour, TFE3 can act as a biomarker in PRCC; moreover, autophagy-inhibiting drugs may have therapeutic effects on TFE3-immunopositive PRCC.

Tumors masquerading as type 2 papillary renal cell carcinoma: pathologists' ever-expanding differential diagnosis for a heterogeneous group of entities

Although papillary renal cell carcinoma has historically been classified as either type 1 or type 2, data from The Cancer Genome Atlas (TCGA) has demonstrated significant genomic heterogeneity in tumors classified as "type 2 papillary renal cell carcinoma" (T2PRCC). Papillary renal cell carcinoma is expected to have a favorable clinical course compared to clear cell renal cell carcinoma (CCRCC). However, tumors with poor outcome more similar to CCRCC were included in the T2PRCC cohort studied by the TCGA. The differential diagnosis for T2PRCC includes a variety of other renal tumors, including aggressive entities such as TFE3 translocation-associated renal cell carcinoma, TFEB-amplified renal cell carcinoma, fumarate hydratase-deficient renal cell carcinoma, high-grade CCRCC, and collecting duct carcinoma. Accurate classification of these tumors is important for prognostication and selection of therapy.

Cathepsin K: A Versatile Potential Biomarker and Therapeutic Target for Various Cancers

Cancer, a common malignant disease, is one of the predominant causes of diseases that lead to death. Additionally, cancer is often detected in advanced stages and cannot be radically cured. Consequently, there is an urgent need for reliable and easily detectable markers to identify and monitor cancer onset and progression as early as possible. Our aim was to systematically review the relevant roles of cathepsin K (CTSK) in various possible cancers in existing studies. CTSK, a well-known key enzyme in the bone resorption process and most studied for its roles in the effective degradation of the bone extracellular matrix, is expressed in various organs. Nowadays, CTSK has been involved in various cancers such as prostate cancer, breast cancer, bone cancer, renal carcinoma, lung cancer and other cancers. In addition, CTSK can promote tumor cells proliferation, invasion and migration, and its mechanism may be related to RANK/RANKL, TGF-β, mTOR and the Wnt/β-catenin signaling pathway. Clinically, some progress has been made with the use of cathepsin K inhibitors in the treatment of certain cancers. This paper reviewed our current understanding of the possible roles of CTSK in various cancers and discussed its potential as a biomarker and/or novel molecular target for various cancers.

Xanthomatous Giant Cell Renal Cell Carcinoma: Another Morphologic Form of TSC-associated Renal Cell Carcinoma

Over the past decade, several distinct novel renal epithelial neoplasms driven by underlying tuberous sclerosis comples (TSC)/mammalian target of rapamycin (MTOR) pathway mutations have been described. We report herein two distinctive TSC2-mutated renal cell carcinomas which do not fit any previously described entity. The two renal carcinomas occurred in young patients (ages 10 and 31 y), and were characterized by highly permeative growth within the kidney with metastases to perirenal lymph nodes. The neoplastic cells were predominantly large, multinucleated giant cells having variably eosinophilic to xanthomatous cytoplasm with basophilic stippling and frequent vacuolization. While the discohesive nature of the neoplastic cells, xanthomatous cytoplasm, immunoreactivity for histiocytic markers and minimal immunoreactivity for conventional epithelial markers raised the possibility of a histiocytic neoplasm, multifocal immunoreactivity for cytokeratin 20 helped establish their epithelial nature. Despite the aggressive growth pattern of these neoplasms and lymph node metastases, mitotic figures were rare and Ki-67 indices were low (<1%). One patient with follow-up shows no evidence of disease seven years after nephrectomy with no adjuvant therapy. Next-generation sequencing demonstrated TSC2 mutations in each case. By immunohistochemistry, downstream markers of mTOR pathway activation S6K1, 4EBP1, and glycoprotein nonmetastatic melanoma protein B were all highly expressed in these neoplasms, suggesting mTOR pathway activation as the neoplastic driver. While the cytokeratin 20 immunoreactivity and focal basophilic cytoplasmic stippling suggest a relationship to eosinophilic solid and cystic renal cell carcinoma, and cytoplasmic vacuolization suggests a relationship to eosinophilic vacuolated tumor, these neoplasms appear to be distinctive given their permeative growth patterns and predominant xanthomatous giant cell morphology. Addition of cytokeratin 20 to a panel of epithelial markers helps avoid misdiagnosis in such cases.

TFE3 Rearrangement and Expression in Renal Cell Carcinoma

TFE3 rearranged Renal cell carcinoma (RCC) is not very common, and demonstrates unique heterogenous morphological features overlapping other recognized entities and distinct immunoprofile. It can be seen in any age group, therefore practicing pathologists should be aware of the distinctive clinical settings and histologic findings associated with these tumors and subsequently employ an adequate panel of ancillary studies in order to confirm the diagnosis. Recognizing these entities remains crucial for future clinical trials and development of novel therapies.

Chameleon TFE3-translocation RCC and How Gene Partners Can Change Morphology: Accurate Diagnosis Using Contemporary Modalities

Translocation renal cell carcinoma (tRCC) with TFE3 gene rearrangements has been born as a distinct entity 20 years ago. These relatively rare tumors were notable among other RCC subtypes because of their disproportionally high incidence among children and young adults. Initial reports were focused on describing unifying morphologic criteria and typical clinical presentation. Follow-up studies of ancillary immunohistochemical and hybridization techniques provided additional diagnostic tools allowing recognition of tRCC tumors in practice. However, a growing body of literature also expanded the clinicomorphologic spectrum of tRCCs, to include a significant morphologic overlap with other RCC variants thus blurring the diagnostic clarity of this entity. More recent molecular studies utilizing next-generation sequencing technology accelerated recognition of numerous novel gene partners fusing at different breakpoints with the TFE3 gene. Accumulating data indicates that morphologic and clinical heterogeneity of tRCC could be explained by fusion subtypes, and knowledge of TFE3 partnering genes may be important in predicting tumor behavior. Herein we provided a comprehensive analysis of ∼400 tRCC cases with known TFE3 fusion partners, estimated their relative incidence and summarized clinicomorphologic features associated with most common fusion subtypes. Our data was based on an extensive literature review and had a special focus on comparing immunohistochemistry, fluorescent in situ hybridization and contemporary molecular studies for the accurate diagnosis of tRCC.

TSC loss is a clonal event in eosinophilic solid and cystic renal cell carcinoma: a multiregional tumor sampling study

Eosinophilic, solid and cystic (ESC) renal cell carcinoma (RCC) is characterized by a solid and cystic architecture with cells showing abundant eosinophilic cytoplasm with hobnail arrangement and a cytokeratin 7-negative/cytokeratin 20-positive immunophenotype. Recent studies have suggested that bi-allelic events affecting TSC genes might play an important role for such tumors. However, only indirect evidence of the clonal origin of TSC mutation has been gathered so far. Therefore, in this paper we aimed to perform multi-regional tumor sampling molecular analysis in four ESC RCC cases that had been completely embedded, three sporadic and one occurring in a patient with tuberous sclerosis complex (TSC). Histologically, the 4 cases showed cystic and solid architecture and cells with abundant eosinophilic cytoplasm with cytoplasmic stippling and round to oval nuclei. Immunohistochemistry showed at least focal expression of cytokeratin 20 in all tissue samples and negative cytokeratin 7, as well as diffuse positivity for S100A1 and at least focal expression of cathepsin K in three out of four cases. The sporadic cases showed the same somatic TSC1 mutations in all tissue samples analyzed, while the TSC-associated case showed the same TSC1 alteration in both normal tissue and all tumor samples analyzed, proving the germline nature of the alteration. In conclusion, our data demonstrate that clonal TSC loss is a key event in ESC RCC and support considering ESC RCC as an entity given its distinct morphologic, immunophenotypical and molecular characteristics.

WHO 2022 Classification of Kidney Tumors: what is relevant? An update and future novelties for the pathologist

Classification systems reflect our technical abilities in the investigation of tumors and our current theories on tumor development. Herein, by providing a historical perspective on the evolution of classifying renal tumors, we assess the current WHO classification highlighting the novelties and the implications of these changes in daily clinical practice.

TFE3 and TFEB-rearranged renal cell carcinomas: an immunohistochemical panel to differentiate from common renal cell neoplasms

TFE3/TFEB-rearranged renal cell carcinomas are characterized by translocations involving TFE3 and TFEB genes. Despite the initial description of typical morphology, their histological spectrum is wide, mimicking common subtypes of renal cell tumors. Thus, the diagnosis is challenging requiring the demonstration of the gene rearrangement, usually by FISH. However, this technique is limited in most laboratories and immunohistochemical TFE3/TFEB analysis is inconsistent. We sought to identify a useful immunohistochemical panel using the most common available markers to recognize those tumors. We performed an immunohistochemical panel comparing 27 TFE3-rearranged and 10 TFEB-rearranged renal cell carcinomas to the most common renal cell tumors (150 clear cell, 100 papillary, 50 chromophobe renal cell carcinomas, 18 clear cell papillary renal cell tumors, and 50 oncocytomas). When dealing with neoplasms characterized by cells with clear cytoplasm, CA9 is a helpful marker to exclude clear cell renal cell carcinoma. GATA3, AMACR, and CK7 are useful to rule out clear cell papillary renal cell tumor. CK7 is negative in TFE3/TFEB-rearranged renal cell carcinoma and positive in papillary renal cell carcinoma, being therefore useful in this setting. Parvalbumin and CK7/S100A1 respectively are of paramount importance when TFE3/TFEB-rearranged renal cell carcinoma resembles oncocytoma and chromophobe renal cell carcinoma. Moreover, in TFEB-rearranged renal cell carcinoma, cathepsin K and melanogenesis markers are constantly positive, whereas TFE3-rearranged renal cell carcinoma stains for cathepsin K in roughly half of the cases, HMB45 in 8% and Melan-A in 22%. In conclusion, since TFE3/TFEB-rearranged renal cell carcinoma may mimic several histotypes, an immunohistochemical panel to differentiate them from common renal cell tumors should include cathepsin K, CA9, CK7, and parvalbumin.

Primary Alveolar Soft Part Sarcoma of Cheek: Report of a Case and Review of the Literature

Alveolar soft part sarcoma (ASPS) is a rare soft tissue sarcoma characterized by an alveolar or organoid arrangement of polygonal tumour cells separated by fibrovascular septa. A specific fusion gene [ASPS critical region 1 (ASPSCR1)-TFE3] was detected in ASPS. Despite being a slow-growing tumour without pain and dysfunction, ASPS is characterized by early metastasis, which leads to poor prognosis. Herein, we report a rare case of primary ASPS of the cheek harbouring ASPSCR1 (exon 7)-TFE3 (exon 5) fusion gene in a 21 year-old woman. This tumour was a well-circumscribed, smooth, round mass that was clinically suspected as a benign tumour. However, histologically, it was observed that the polygonal tumour cells were arranged in solid and alveolar growth patterns. Post-operative examination of the whole body excluded the possibility of metastasis at other sites. Thus, careful immunohistochemical and genetic analyses, as well as whole-body examination, demonstrated that the tumour was a primary ASPS of the cheek.

Translocation carcinomas of the kidney

The MiT subfamily of transcription factors includes TFE3, TFEB, TFEC, and MITF. Gene fusions involving two of these transcription factors have been well-characterized in renal cell carcinoma (RCC). The TFE3-rearranged RCC (also known as Xp11 translocation RCC) was first officially recognized in the 2004 World Health Organization (WHO) renal tumor classification. The TFEB-rearranged RCC, which typically harbor a t(6;11)(p21;q12) translocation which results in a MALAT1-TFEB gene fusion, were first officially recognized in the 2016 WHO renal tumor classification. These two subtypes of translocation RCC have many similarities. Both disproportionately involve young patients, although adult translocation RCC overall outnumber pediatric cases. Both often have unusual and distinctive morphologies; the TFE3-rearranged RCCs frequently have clear cells with papillary architecture and abundant psammoma bodies, while the TFEB-rearranged RCCs frequently have a biphasic appearance with both small and large epithelioid cells and nodules of basement membrane material. However, the morphology of these two neoplasms can overlap, with one mimicking the other or other more common renal neoplasms. Both of these RCC underexpress epithelial immunohistochemical markers, such as cytokeratin and epithelial membrane antigen, relative to most other RCC. Unlike other RCC, both frequently express the cysteine protease cathepsin k and often express melanocytic markers like HMB45 and Melan A. Finally, TFE3 and TFEB have overlapping functional activity as these two transcription factors frequently heterodimerize and bind to the same targets. Therefore, these two neoplasms are now grouped together under the heading of "MiT family translocation RCC." Approximately 50 renal cell carcinomas with gene fusions involving the anaplastic lymphoma kinase (ALK) gene have now been reported. While those with a Vinculin-ALK fusion have distinctive features (predilection to affect children with sickle cell trait and to show solid architecture with striking cytoplasmic vacuolization), other ALK-fusion RCCs have more varied clinical presentations and pathologic features. This review summarizes our current knowledge of these recently described RCC.

The Morphological Spectrum of Papillary Renal Cell Carcinoma and Prevalence of Provisional/Emerging Renal Tumor Entities with Papillary Growth

Renal cell carcinoma (RCC) represents a heterogeneous disease, encompassing an increasing number of tumor subtypes. Post-2016, the World Health Organization (WHO) classification recognized that the spectrum of papillary renal cell carcinoma is evolving and has long surpassed the dichotomic simplistic "type 1 versus type 2" classification. The differential diagnosis of pRCC includes several new provisional/emerging entities with papillary growth. Type 2 tumors have been cleared out of several confounding entities, now regarded as independent tumors with specific clinical and molecular backgrounds. In this work we describe the prevalence and characteristics of emerging papillary tumor entities in two renal tumor cohorts (one consisting of consecutive papillary tumors from a single institute, the other consisting of consultation cases from several centers). After a review of 154 consecutive pRCC cases, 58% remained type 1 pRCC, and 34% type 2 pRCC. Papillary renal neoplasm with reversed polarity (1.3%), biphasic hyalinizing psammomatous RCC (1.3%), and biphasic squamoid/alveolar RCC (4.5%) were rare. Among 281 consultation cases, 121 (43%) tumors had a dominant papillary growth (most frequently MiT family translocation RCCs, mucinous tubular and spindle cell carcinoma and clear cell papillary RCC). Our data confirm that the spectrum of RCCs with papillary growth represents a major diagnostical challenge, frequently requiring a second expert opinion. Papillary renal neoplasm with reversed polarity, biphasic hyalinizing psammomatous RCC, and biphasic squamoid/alveolar RCC are rarely sent out for a second opinion, but correct classification and knowledge of these variants will improve our understanding of the clinical behavior of renal tumors with papillary growth.

Mesenchymal Tumors of the Mediastinum: An Update on Diagnostic Approach

Mesenchymal tumors of the mediastinum are a heterogenous group of rare tumors with divergent lineages. Mediastinal mesenchymal tumors are diagnostically challenging due to their diversity and morphologic overlap with nonmesenchymal lesions arising in the mediastinum. Accurate histologic diagnosis is critical for appropriate patient management and prognostication. Many mediastinal mesenchymal tumors affect distinct age groups or occur at specific mediastinal compartments. Neurogenic tumors, liposarcoma, solitary fibrous tumor, and synovial sarcoma are common mesenchymal tumors in the mediastinum. Herein, we provide an update on the diagnostic approach to mediastinal mesenchymal tumors and a review of the histologic features and differential diagnosis of common benign and malignant mesenchymal tumors of the mediastinum.

TRIM63 is a sensitive and specific biomarker for MiT family aberration-associated renal cell carcinoma

Microphthalmia-associated transcription factor (MiT) family aberration-associated renal cell carcinoma (MiTF-RCC) is a subtype of renal cell carcinoma harboring recurrent chromosomal rearrangements involving TFE3 or TFEB genes. MiTF-RCC is morphologically diverse, can histologically resemble common RCC subtypes like clear cell RCC and papillary RCC, and often poses a diagnostic challenge in genitourinary clinical and pathology practice. To characterize the MiTF-RCC at the molecular level and identify biomarker signatures associated with MiTF-RCC, we analyzed RNAseq data from MiTF-RCC, other RCC subtypes and benign kidney. Upon identifying TRIM63 as a cancer-specific biomarker in MiTF-RCC, we evaluated its expression independently by RNA in situ hybridization (RNA-ISH) in whole tissue sections from 177 RCC cases. We specifically included 31 cytogenetically confirmed MiTF-RCC cases and 70 RCC cases suspicious for MiTF-RCC in terms of clinical and morphological features, to evaluate and compare TRIM63 RNA-ISH results with the results from TFE3/TFEB fluorescence in situ hybridization (FISH), which is the current clinical standard. We confirmed that TRIM63 mRNA was highly expressed in all classes of MiTF-RCC compared to other renal tumor categories, where it was mostly absent to low. While the TRIM63 RNA-ISH and TFE3/TFEB FISH results were largely concordant, importantly, TRIM63 RNA-ISH was strongly positive in TFE3 FISH false-negative cases with RBM10-TFE3 inversion. In conclusion, TRIM63 can serve as a diagnostic marker to distinguish MiTF-RCC from other renal tumor subtypes with overlapping morphology. We suggest a combination of TFE3/TFEB FISH and TRIM63 RNA-ISH assays to improve the accuracy and efficiency of MiTF-RCC diagnosis. Accurate diagnosis of MiTF-RCC and other RCC subtypes would enable effective targeted therapy and avoid poor therapeutic response due to tumor misclassification.

Kidney cancer: from genes to therapy

Renal cell carcinoma incidence is rising worldwide with increasing subtype stratification by the World Health Organization. Each subtype has unique genetic alterations, cell biology changes and clinical findings. Such genetic alterations offer the potential for individualized therapeutic approaches that are rapidly progressing. This review highlights the most common subtypes of renal cell carcinoma, including both hereditary and sporadic forms, with a focus on genetic changes, clinical findings and ongoing clinical trials.

Key Renal Neoplasms With a Female Predominance

Renal neoplasms largely favor male patients; however, there is a growing list of tumors that are more frequently diagnosed in females. These tumors include metanephric adenoma, mixed epithelial and stromal tumor, juxtaglomerular cell tumor, mucinous tubular and spindle cell carcinoma, Xp11.2 (TFE3) translocation-associated renal cell carcinoma, and tuberous sclerosis complex (somatic or germline) associated renal neoplasms. The latter category is a heterogenous group with entities still being delineated. Eosinophilic solid and cystic renal cell carcinoma is the best-described entity, whereas, eosinophilic vacuolated tumor is a proposed entity, and the remaining tumors are currently grouped together under the umbrella of tuberous sclerosis complex/mammalian target of rapamycin-related renal neoplasms. The entities described in this review are often diagnostic considerations when evaluating renal mass tissue on biopsy or resection. For example, Xp11.2 translocation renal cell carcinoma is in the differential when a tumor has clear cell cytology and papillary architecture and occurs in a young or middle-aged patient. In contrast, tuberous sclerosis complex-related neoplasms often enter the differential for tumors with eosinophilic cytology. This review provides an overview of the clinical, gross, microscopic, immunohistochemical, genetic, and molecular alterations in key renal neoplasms occurring more commonly in females; differential diagnoses are also discussed regardless of sex predilection.

New developments in existing WHO entities and evolving molecular concepts: The Genitourinary Pathology Society (GUPS) update on renal neoplasia

The Genitourinary Pathology Society (GUPS) reviewed recent advances in renal neoplasia, particularly post-2016 World Health Organization (WHO) classification, to provide an update on existing entities, including diagnostic criteria, molecular correlates, and updated nomenclature. Key prognostic features for clear cell renal cell carcinoma (RCC) remain WHO/ISUP grade, AJCC/pTNM stage, coagulative necrosis, and rhabdoid and sarcomatoid differentiation. Accrual of subclonal genetic alterations in clear cell RCC including SETD2, PBRM1, BAP1, loss of chromosome 14q and 9p are associated with variable prognosis, patterns of metastasis, and vulnerability to therapies. Recent National Comprehensive Cancer Network (NCCN) guidelines increasingly adopt immunotherapeutic agents in advanced RCC, including RCC with rhabdoid and sarcomatoid changes. Papillary RCC subtyping is no longer recommended, as WHO/ISUP grade and tumor architecture better predict outcome. New papillary RCC variants/patterns include biphasic, solid, Warthin-like, and papillary renal neoplasm with reverse polarity. For tumors with 'borderline' features between oncocytoma and chromophobe RCC, a term "oncocytic renal neoplasm of low malignant potential, not further classified" is proposed. Clear cell papillary RCC may warrant reclassification as a tumor of low malignant potential. Tubulocystic RCC should only be diagnosed when morphologically pure. MiTF family translocation RCCs exhibit varied morphologic patterns and fusion partners. TFEB-amplified RCC occurs in older patients and is associated with more aggressive behavior. Acquired cystic disease (ACD) RCC-like cysts are likely precursors of ACD-RCC. The diagnosis of renal medullary carcinoma requires a negative SMARCB1 (INI-1) expression and sickle cell trait/disease. Mucinous tubular and spindle cell carcinoma (MTSCC) can be distinguished from papillary RCC with overlapping morphology by losses of chromosomes 1, 4, 6, 8, 9, 13, 14, 15, and 22. MTSCC with adverse histologic features shows frequent CDKN2A/2B (9p) deletions. BRAF mutations unify the metanephric family of tumors. The term "fumarate hydratase deficient RCC" ("FH-deficient RCC") is preferred over "hereditary leiomyomatosis and RCC syndrome-associated RCC". A low threshold for FH, 2SC, and SDHB immunohistochemistry is recommended in difficult to classify RCCs, particularly those with eosinophilic morphology, occurring in younger patients. Current evidence does not support existence of a unique tumor subtype occurring after chemotherapy/radiation in early childhood.

Uncommon Localization of Extrarenal Xp11.2 Translocation-associated Renal Cell Carcinoma (RCC): Case Report

The World Health Organization has recognized Xp11.2 translocation-associated renal cell carcinoma (RCC) as a distinct neoplasm that arises within the kidney. Although many reports of extrarenal carcinoma may be found in the literature, to the best of our knowledge, Xp11 translocation-associated RCC with intact kidneys has not been documented. This report describes a multilobulated right retroperitoneal soft tissue mass (7.9×5.3×12.6 cm) of a 37-year-old man complaining of abdominal pain in the right side. The patient underwent a computed tomography-guided biopsy. Microscopic evaluation reveals a tumor with papillary and sheaths architectures with cells revealing clear to eosinophilic cytoplasm. Immunohistochemical evaluation on the biopsy reveals that the tumor is positive for PAX-8, CD10, and TFE3. It is negative for CK7, EMA, Vimentin, RCC, CK8/18, D20, CD3, PLAP, OCT4, CD30, MART-1, Inhibin, S-100, HMB-45, Desmin, SMA, and DOG-1. The diagnosis was malignant epithelioid neoplasm and the diagnosis of translocation RCC was suggested. Excision was recommended. The patient underwent right radical nephrectomy with removal of this large mass. Pathologic examination showed a large cystic and solid, nonhomogenous mass with some necrotic areas, originating from the perirenal fat between the adrenal gland and the kidney. Microscopic features showed a tumor with papillary, rhabdoid, and clear cell features. Immunohistochemical stains showed that the tumor cells positively expressed AMACR, PAX-8, CD10, RCC, and TFE3, but were negative for cytokeratins, vimentin, HMB-45, desmin, SMA, EMA, and MSA. Cytogenetic studies confirmed the diagnosis of Xp11.2 translocation-associated RCC with positive TFE3 gene rearrangement. To the best of our knowledge, this type of extrarenal tumor has never been reported.

Cathepsin K: A Novel Diagnostic and Predictive Biomarker for Renal Tumors

Simple Summary

Our understanding of renal tumors has increased in the last years with the description of several novel entities. The expanding morphological spectrum complicates the pathologist’s diagnosis, often requiring immunohistochemical analysis. The role of cathepsin K immunoexpression is widened as a diagnostic tool in several renal tumors. This review describes the usefulness of cathepsin K in the differential diagnosis of renal neoplasms, highlighting the biological knowledge underpinning its expression. Moreover, cathepsin K seems to be a downstream marker of different genetic alterations, with a possible role as a predictive marker that may prospectively guide the development of therapeutic approaches as a molecular target.

Abstract

Cathepsin K is a papain-like cysteine protease with high matrix-degrading activity. Among several cathepsins, cathepsin K is the most potent mammalian collagenase, mainly expressed by osteoclasts. This review summarizes most of the recent findings of cathepsin K expression, highlighting its role in renal tumors for diagnostic purposes and as a potential molecular target. Indeed, cathepsin K is a recognized diagnostic tool for the identification of TFE3/TFEB-rearranged renal cell carcinoma, TFEB-amplified renal cell carcinoma, and pure epithelioid PEComa/epithelioid angiomyolipoma. More recently, its expression has been observed in a subgroup of eosinophilic renal neoplasms molecularly characterized by TSC/mTOR gene mutations. Interestingly, both TSC mutations or TFE3 rearrangement have been reported in pure epithelioid PEComa/epithelioid angiomyolipoma. Therefore, cathepsin K seems to be a downstream marker of TFE3/TFEB rearrangement, TFEB amplification, and mTOR pathway activation. Given the established role of mTOR inhibitors as a pharmacological option in renal cancers, cathepsin K could be of use as a predictive marker of therapy response and as a potential target. In the future, uropathologists may implement the use of cathepsin K to establish a diagnosis among renal tumors with clear cells, papillary architecture, and oncocytic features.

Contemporary Characterization and Recategorization of Adult Unclassified Renal Cell Carcinoma

Our recent study of early-onset unclassified eosinophilic renal cell carcinoma (RCC) demonstrated that two third of cases could be reclassified by performing a limited number of immunohistochemistry stains. Following the same approach, we aimed to investigate what proportion of adult unclassified RCC could be reclassified. We identified 79 cases. The mean age at presentation was 58 years (range, 29 to 84 y). Tumors were grouped based on their predominant morphologic features as oncocytic (n=23); papillary (n=22); clear cell (n=22); mucinous tubular and spindle cell (MTSC; n=5); rhabdoid (n=4); or lacking a dominant pattern (n=3). By reviewing the morphologic features and performing ancillary studies, we were able to reclassify 10 cases (13%). Four cases were positive for CK20 and showed morphologic features consistent with eosinophilic solid and cystic RCC. Four cases were reclassified as MTSC based on VSTM2A expression by RNA in situ hybridization. One case was negative for SDHB and reclassified as succinate dehydrogenase-deficient RCC. None of the cases showed loss of expression of fumarate hydratase. One case was diffusely positive for CK7 and negative for CD117 and reclassified as a low-grade oncocytic tumor. Four cases were positive for both cathepsin-K and TFE3 by immunohistochemistry, although fluorescence in situ hybridization failed to identify rearrangement in either TFE3 or TFEB genes. Of the tumors that remained unclassified, those with oncocytic features were less likely to be a high grade (odds ratio [OR]=0.22, P=0.013) or advanced stage (OR=0.19, P=0.039) and were more common in women (OR=3.4, P=0.05) compared with those without oncocytic features. Tumors with rhabdoid morphology were associated with advanced stage (relative risk=3.6, P=0.009), while tumors with clear cell or papillary features had a wide range of grades and stages at presentation. In summary, the most frequent reclassified entity is eosinophilic solid and cystic RCC. Investigation of expression of succinate dehydrogenase or fumarate hydratase in individuals older than 35 years with unclassifiable tumors is low yield in the absence of specific morphologic features. A subset of MTSC without well-developed morphologic features can be reclassified by using RNA-ISH for VSTM2A. Recognition of more-recently described RCC subtypes allows for their distinction from the unclassified subtype and improves the prognostic information provided.

Alveolar Soft Part Sarcoma of Uterine Corpus in a Young Female: A Case Report With Review of Literature

Alveolar soft part sarcoma (ASPS) is a rare soft tissue sarcoma, often occurs in adolescents and young adults with a particular predilection for the deep soft tissue of extremities. Occurrence of ASPS in the female genital tract is very uncommon and poses a significant diagnostic challenge. A case of ASPS of the uterine corpus is described in a young unmarried female, who presented to the out-patient clinic of our Institute with complaints of abnormal uterine bleeding for the past 9 mo. She was being treated with oral contraceptive pills, progesterone and tranexamic acid. Following radiological imaging and hysteroscopy, a therapeutic curettage of the lesion was done. The histopathologic features raised a differential diagnosis of a myriad of morphologic mimickers. The diagnosis was clinched by exclusion of mimickers by relevant immunohistochemical markers and strong nuclear expression of TFE3 on immunohistochemistry. The patient is on regular follow-up with oral contraceptives and antifibrinolytic medication. Despite being infrequent at this location, ASPS should be kept in differential diagnosis in young females presenting with abnormal uterine bleeding.

Cathepsin K (Clone EPR19992) Demonstrates Uniformly Positive Immunoreactivity in Renal Oncocytoma, Chromophobe Renal Cell Carcinoma, and Distal Tubules

Introduction. Cathepsin K is overexpressed in several tumors associated with microphthalmia transcription factor (MiTF) family or mechanistic target of rapamycin (mTOR) upregulation. Among renal neoplasms, MiTF translocation renal cell carcinoma (RCC), perivascular epithelioid cell neoplasms (PEComa), and eosinophilic solid and cystic RCC have demonstrated Cathepsin K immunoreactivity. In this study, we demonstrate a uniform Cathepsin K expression in oncocytoma, chromophobe RCC (CHRCC), and distal tubules. Design. We stained 13 oncocytomas, 13 CHRCC, 14 clear cell RCC (CCRCC), 9 papillary RCC (PRCC), 9 PEComas, and 5 MiTF RCC. Additionally, we assessed immunoreactivity for Cathepsin K in non-neoplastic renal parenchyma. Immunolabeling was performed on regularly charged slides from formalin-fixed paraffin-embedded tissue with monoclonal anti-rabbit antibodies to human Cathepsin K (clone EPR19992, Abcam). Results. All oncocytomas demonstrated diffuse strong cytoplasmic immunolabeling. CHRCC demonstrated uniform less intense immunolabeling in all cases with membranous accentuation. The assessment of the non-neoplastic renal parenchyma in all cases showed strong cytoplasmic immunoreaction in distal tubules and proximal tubules stained faintly. Mesangial cells were not immunoreactive. All MiTF RCC and PEComas were immunoreactive for Cathepsin K, whereas CCRCC and PRCC were negative in all cases. Conclusions. In this study, we expand the spectrum of renal neoplasms reactive with a particular clone of Cathepsin K (EPR19992). Distal tubules are strongly immunoreactive for Cathepsin K. Our conclusions need to be taken into consideration when differential diagnosis includes MiTF RCC or PEComa and this Cathepsin K clone is included in the immunohistochemical panel. This newer antibody clone was not tested in prior publications, potentially explaining the difference in conclusions.

[Molecular pathology of urogenital tumors : Recommendations from the 2019 International Society of Urological Pathology (ISUP) Consensus Conference]

Das zunehmende Verständnis molekularer Grundlagen von Tumoren sowie der Fortschritt in der Diversifizierung der onkologischen Therapien versprechen individualisierte Therapieoptionen, welche bislang jedoch nur ansatzweise in die Therapieplanung von urologischen Tumoren eingegangen sind. Daher hat die Internationale Gesellschaft für Urologische Pathologie (ISUP) im März 2019 eine Konsenskonferenz zur Erarbeitung evidenzbasierter Handlungsempfehlungen zur molekularpathologischen Diagnostik beim Urothelkarzinom, Nierenzellkarzinom, Prostatakarzinom, Peniskarzinom und testikulären Keimzelltumoren durchgeführt. Die auf dieser Konsenskonferenz erarbeiteten Empfehlungen sind kürzlich in 5 separaten Manuskripten veröffentlich worden und werden in der vorliegenden Arbeit zusammengefasst.

Im Rahmen der Konferenzvorbereitung wurde eine umfassende Umfrage zur derzeitigen Praxis molekularer Testungen bei urogenitalen Tumoren unter den Mitgliedern der ISUP durchgeführt. Auf der Konferenz wurden die Ergebnisse und die entsprechenden Hintergrundinformationen durch 5 Arbeitsgruppen präsentiert und Handlungsempfehlungen für die Diagnostik erarbeitet. Eine Übereinstimmung von 66 % der Konferenzteilnehmer wurde als Konsens definiert.

Clinicopathological Findings on 28 Cases with XP11.2 Renal Cell Carcinoma

Xp11.2 translocation carcinoma is a distinct subtype of renal cell carcinoma characterized by translocations involving the TFE3 gene. Our study included the morphological, immunohistochemical and clinicopathological examination of 28 Xp11.2 RCCs. The immunophenotype has been assessed by using CA9, CK7, CD10, AMACR, MelanA, HMB45, Cathepsin K and TFE3 immunostainings. The diagnosis was confirmed by TFE3 break-apart FISH in 25 cases. The ages of 13 male and 15 female patients, without underlying renal disease or having undergone chemotherapy ranged from 8 to 72. The mean size of the tumors was 78.5 mm. Forty-three percent of patients were diagnosed in the pT3/pT4 stage with distant metastasis in 6 cases. Histological appearance was branching-papillary composed of clear cells with voluminous cytoplasm in 13 and variable in 15 cases, including one tumor with anaplastic carcinoma and another with rhabdoid morphology. Three tumors were labeled with CA9, while CK7 was negative in all cases. Diffuse CD10 reaction was observed in 17 tumors and diffuse AMACR positivity was described in 14 tumors. The expression of melanocytic markers and Cathepsin K were seen only in 7 and 6 cases, respectively. TFE3 immunohistochemistry displayed a positive reaction in 26/28 samples. TFE3 rearrangement was detected in all the analyzed cases (25/25), including one with the loss of the entire labeled break-point region. The follow-up time ranged from 2 to 300 months, with 7 cancer-related deaths. In summary, Xp11.2 carcinoma is an uncommon form of renal cell carcinoma with a variable histomorphology and rather aggressive clinical course.

Cytological diagnosis of Xp11 translocation renal cell carcinoma: An unusual suspect in bone metastases from unknown primary malignancies

BACKGROUND

Renal cell carcinoma (RCC) constitutes 3% of all cancers, with a higher incidence in patients with age between 60 and 70 years. RCC frequently present as a metastatic tumor at diagnosis, and bones represent one of the most frequent sites. Many cases, mainly in young patients, includes the Xp11 translocation RCC. The cytological diagnosis of Xp11 translocation RCC in adult population it is rarely performed, likely for the morphological overlap with other adult renal cell carcinoma subtypes.

METHODS

We retrospectively analyze a series of 92 adult patients with metastatic bone tumors, diagnosed on fine-needle aspiration cytology (FNAC) samples, focusing mainly on the cytological, immunophenotypic and molecular features of Xp11 translocation RCC.

RESULTS

In our series 6 of 92 (6.5%) cases were metastatic RCC (mRCC), among them 2 cases were metastasis from Xp11translocation RCC. Those cases showed a bloody background, with several groups of atypical cells arranged in syncytial groups or in papillary groups composed by atypical cells with abundant cytoplasm, with scattered clear cells. TFE3 was positive on immunocytochemical analysis and specific translocation t(Xp11.23) was detected by FISH analysis.

CONCLUSIONS

In adult patients with mRCC, it is necessary to consider also Xp11 translocation RCC among the diagnostic hypotheses. FNAC represents a valid tool to investigate bone lesions but cytological features of Xp11 translocation RCC are still poorly described and must necessarily be better defined.

Xp11.2 translocation renal cell carcinoma with TFE3 gene fusion in the elderly: case report and literature review

A 68-year-old man was followed up with chronic kidney disease. Follow-up CT incidentally detected a tumor at the left kidney and multiple small nodular shadows in the lungs bilaterally. The patient underwent needle biopsy and was diagnosed with Xp11.2 translocation renal cell carcinoma (RCC) pathologically. Hence, laparoscopic nephrectomy was performed. Fluorescence in situ hybridization analysis revealed a break-apart of the transcription factor E3 (TFE3) genes in the left tumor. After 2 months postoperatively, nivolumab and ipilimumab were administered thrice intravenously, considering the intermediate risk by the IMDC risk classification. However, pleural effusion occurred but was removed adequately. Lung metastasis decreased, but new metastasis occurred at the left iliopsoas muscle. Target therapy was performed with axitinib. Unfortunately, he died 6 months later postoperatively. These tumors commonly occur in children than in adults, and very rare in elderly patients. Xp11.2 translocation RCC in the elderly has a poorer prognosis than that in children. To date, no effective treatment for Xp11.2 translocation RCC has been established.

Report From the International Society of Urological Pathology (ISUP) Consultation Conference on Molecular Pathology of Urogenital Cancers: III: Molecular Pathology of Kidney Cancer

Renal cell carcinoma (RCC) subtypes are increasingly being discerned via their molecular underpinnings. Frequently this can be correlated to histologic and immunohistochemical surrogates, such that only simple targeted molecular assays, or none at all, are needed for diagnostic confirmation. In clear cell RCC, VHL mutation and 3p loss are well known; however, other genes with emerging important roles include SETD2, BAP1, and PBRM1, among others. Papillary RCC type 2 is now known to include likely several different molecular entities, such as fumarate hydratase (FH) deficient RCC. In MIT family translocation RCC, an increasing number of gene fusions are now described. Some TFE3 fusion partners, such as NONO, GRIPAP1, RBMX, and RBM10 may show a deceptive fluorescence in situ hybridization result due to the proximity of the genes on the same chromosome. FH and succinate dehydrogenase deficient RCC have implications for patient counseling due to heritable syndromes and the aggressiveness of FH-deficient RCC. Immunohistochemistry is increasingly available and helpful for recognizing both. Emerging tumor types with strong evidence for distinct diagnostic entities include eosinophilic solid and cystic RCC and TFEB/VEGFA/6p21 amplified RCC. Other emerging entities that are less clearly understood include TCEB1 mutated RCC, RCC with ALK rearrangement, renal neoplasms with mutations of TSC2 or MTOR, and RCC with fibromuscular stroma. In metastatic RCC, the role of molecular studies is not entirely defined at present, although there may be an increasing role for genomic analysis related to specific therapy pathways, such as for tyrosine kinase or MTOR inhibitors.

Comprehensive analysis of 34 MiT family translocation renal cell carcinomas and review of the literature: investigating prognostic markers and therapy targets

Recently cabozantinib, a tyrosine kinase inhibitor with activity against VEGF, MET, AXL, and downregulating cathepsin K in vitro, has been proposed for the treatment of advanced clear and non-clear renal cell carcinomas. Since it is well known that cathepsin K is expressed in the majority of MiT family translocation renal cell carcinomas, we investigated cathepsin K, MET, AXL, and VEGF in a large series of those tumours, looking for possible predictive markers. We collected the clinicopathological features of 34 genetically confirmed MiT family translocation renal cell carcinomas [26 Xp11 and 8 t(6;11) renal cell carcinomas] and studied them using an immunohistochemical panel including PAX8, cathepsin K, HMB45, Melan-A, CD68 (PG-M1), CK7, CA9, MET, AXL and by FISH for VEGFA and MET. Cathepsin K was expressed in 14 of 26, HMB45 in 8 of 25, and Melan-A in 4 of 23 Xp11 renal cell carcinomas, whereas labelling for CK7 and CA9 was minimal. In t(6;11) renal cell carcinoma, cathepsin K and melanogenesis markers were constantly positive, whereas CK7 and CA9 were negative. None of the 34 carcinomas showed CD68 (PG-M1) and AXL expression. One aggressive Xp11 renal cell carcinoma showed increased VEGFA gene copy number (4-5 copies) with concurrent gains of TFE3 and TFEB. None of the 34 carcinomas showed MET gene amplification, whereas staining for MET was found in 7 of 8 t(6;11) and in 16 of 24 Xp11 renal cell carcinomas, and in the latter cases, when the expression was >50%, correlated with aggressiveness (p=0.0049). In Xp11 renal cell carcinomas, the aggressiveness was also correlated with larger tumour size (p=0.0008) and the presence of necrosis (p=0.027) but not nucleolar grading (p=1). Interestingly, in patients with tumours exhibiting two of three parameters (necrosis, larger tumour size and MET immunolabelling >50%) an aggressive clinical behaviour was observed in 88% of cases. In conclusion, cathepsin K, CD68 (PG-M1), CK7, CA9, and PAX8 is a useful panel for the diagnosis. Larger tumour size, the presence of necrosis and MET immunohistochemical expression correlate with aggressive behaviour in Xp11 renal cell carcinomas, especially in combination. VEGF, MET, cathepsin K but not AXL may be potential predictive markers for targeted therapy in MiT family translocation renal cell carcinomas.

Renal Tumors of Childhood-A Histopathologic Pattern-Based Diagnostic Approach

Renal tumors comprise approximately 7% of all malignant pediatric tumors. This is a highly heterogeneous group of tumors, each with its own therapeutic management, outcome, and association with germline predispositions. Histopathology is the key in establishing the correct diagnosis, and therefore pathologists with expertise in pediatric oncology are needed for dealing with these rare tumors. While each tumor shows different histologic features, they do have considerable overlap in cell type and histologic pattern, making the diagnosis difficult to establish, if based on routine histology alone. To this end, ancillary techniques, such as immunohistochemistry and molecular analysis, can be of great importance for the correct diagnosis, resulting in appropriate treatment. To use ancillary techniques cost-effectively, we propose a pattern-based approach and provide recommendations to aid in deciding which panel of antibodies, supplemented by molecular characterization of a subset of genes, are required.

Alveolar soft part sarcoma presenting as a uterine polyp: A case report

Alveolar soft part sarcoma is a rare malignant soft tissue tumor, mainly localized in the extremities and occurring principally in adolescents and young adults. Alveolar soft part sarcoma are uncommon in the female genital tract. We here report a case of alveolar soft part sarcoma in a 20-year-old nullipara, presenting with vaginal bleeding and profound anemia requiring blood transfusions. Ultrasonographic examination revealed a polyp in the lower uterine segment. Surgical resection of the polyp was performed, and pathological evaluation showed typical histological, immunohistochemical, and molecular features consistent with alveolar soft part sarcoma. Patient underwent for total hysterectomy. Currently, she follows up with her surgeon and has no new complains. Given the infrequency of alveolar soft part sarcoma, this case report raises the awareness of alveolar soft part sarcoma as one of the entities to consider when confronted with a uterine polyp in a young patient.

[MiT family translocation renal cell carcinomas: Natural history, molecular features and multidisciplinary management]

MiT family translocation renal cell carcinomas (tRCC) represent a rare subtype of renal cell carcinomas. These tumors have been introduced for the first time in the World Health Classification (WHO) classification of kidney cancers in 2004. tRCC are characterized by reccurent translocations involving members of the MiT family transcription factors, mainly TFE3 and TFEB. The estimated incidence of these tumors is ∼1-5 % among all renal cell carcinomas, with female prodominance. tRCC were initially described in children, and the spectrum has been expanded over time to encompass adolescents and adults. TFE3- and TFEB-rearranged RCC harbor characteristic clinicopathological and immunohistochemical features and fluorescent hybridization in situ is considered the gold standard for their diagnosis, although it has some limitations especially when the partners are located in the vicinity of TFE3. Nephron-sparing surgery is an efficient treatment of localized cases when achievable. In metastatic setting, targeted agents and immunotherapy showed modest efficacy, with response rates and median overall survival inferior to those observed in clear-cell renal cell carcinomas. Management of tRCC necessite a multidisciplinary team and accrual in clinical trials have to be encouraged when possible. Novel biological insights are urgently awaited to better understand the mechanisms associated with kidney oncogenesis in this setting, and ultimately help to identify therapeutic targets.

Expanding the morphologic spectrum of chromophobe renal cell carcinoma: A study of 8 cases with papillary architecture

Although typically arranged in solid alveolar fashion, chromophobe renal cell carcinoma (RCC) may also show several other architectural growth patterns. We include in this series 8 chromophobe RCC cases with prominent papillary growth, a pattern very rarely reported or only mentioned as a feature of chromophobe RCC, which is lacking wider recognition The differential diagnosis of such cases significantly varies from the typical chromophobe RCC with its usual morphology, particularly its distinction from papillary RCC and other relevant and clinically important entities. Of 972 chromophobe RCCs in our files, we identified 8 chromophobe RCCs with papillary growth. We performed immunohistochemistry and array Comparative Genomic Hybridisation (aCGH) to investigate for possible chromosomal aberrations. Patients were 3 males and 5 females with age ranging from 30 to 84 years (mean 57.5, median 60 years). Tumor size was variable and ranged from 2 to 14 cm (mean 7.5, median 6.6 cm). Follow-up was available for 7 of 8 patients, ranging from 1 to 61 months (mean 20.1, median 12 months). Six patients were alive with no signs of aggressive behavior, and one died of the disease. Histologically, all cases were composed of dual cell population consisting of variable proportions of leaf-like cells with pale cytoplasm and eosinophilic cells. The extent of papillary component ranged from 15 to 100% of the tumor volume (mean 51%, median 50%). Sarcomatoid differentiation was identified only in the case with fatal outcome. Immunohistochemically, all tumors were positive for CK7, CD117 and Hale's Colloidal Iron. PAX8 was positive in 5 of 8 cases, TFE3 was focally positive 3 of 8 tumors, and Cathepsin K was focally positive in 2 of 8 tumors. All cases were negative for vimentin, AMACR and HMB45. Fumarate hydratase staining was retained in all tested cases. The proliferative activity was low (up to 1% in 7, up to 5% in one case). Three cases were successfully analyzed by aCGH and all showed a variable copy number variation profile with multiple chromosomal gains and losses. CONCLUSIONS: Chromophobe RCC demonstrating papillary architecture is an exceptionally rare carcinoma. The diagnosis can be challenging, although the cytologic features are consistent with the classic chromophobe RCC. Given the prognostic and therapeutic implications of accurately diagnosis other RCCs with papillary architecture (i.e., Xp11.2 translocation RCC, FH-deficient RCC), it is crucial to differentiate these cases from chromophobe RCC with papillary architecture. Based on this limited series, the presence of papillary architecture does not appear to have negative prognostic impact. However, its wider recognition may allow in depth studies on additional examples of this rare morphologic variant.

A Rare Partner of TFE3 in the Xp11 Translocation Renal Cell Carcinoma: Clinicopathological Analyses and Detection of MED15-TFE3 Fusion

Xp11 translocation renal cell carcinoma (RCC), a member of the microphthalmia-associated transcription factor (MiTF) family, is a rare renal tumor characterized by different translocations involving the TFE3 gene. Here, we reported a case of Xp11 translocation RCC with a rare MED15-TFE3 gene fusion by RNA sequencing. Morphologically, the tumor cells were arranged in a solid and small nest pattern. The cytoplasm was voluminous, flocculent eosinophilic, and vacuolated. The nuclei were round or polygon with fine granular chromatin, and the nucleoli were unconspicuous. Psammoma bodies were observed in mesenchyma. Immunohistochemically, the tumor cells were diffuse moderately or strongly positive for CD10, P504S, vimentin, PAX8, RCC, AE1/AE3, and SDHB and focally positive for CK7 and CA IX while negative for cathepsin K, HMB45, Melan-A, Ksp-cadherin, and CD117. The Ki67 proliferation index was approximately 3%. However, TFE3 labeling showed an uncertainly weak nuclear staining and been considered negative. Fluorescence in situ hybridization (FISH) demonstrated a positive result that splits signals with a distance of > 2 signal diameters. Subsequently, RNA sequencing confirmed a fusion of MED15 gene exon 11 on chromosome 22 with TFE3 gene exon 6 in the tumor. The patient was alive with no evidence of recurrence. Our report contributes to the understanding on MED15-TFE3 RCC.

MiT Family Translocation Renal Cell Carcinoma: from the Early Descriptions to the Current Knowledge

The new category of MiT family translocation renal cell carcinoma has been included into the World Health Organization (WHO) classification in 2016. The MiT family translocation renal cell carcinoma comprises Xp11 translocation renal cell carcinoma harboring TFE3 gene fusions and t(6;11) renal cell carcinoma harboring TFEB gene fusion. At the beginning, they were recognized in childhood; nevertheless, it has been demonstrated that these neoplasms can occur in adults as well. In the nineties, among Xp11 renal cell carcinoma, ASPL, PRCC, and SFPQ (PSF) were the first genes recognized as partners in TFE3 rearrangement. Recently, many other genes have been identified, and a wide spectrum of morphologies has been described. For this reason, the diagnosis may be challenging based on the histology, and the differential diagnosis includes the most common renal cell neoplasms and pure epithelioid PEComa/epithelioid angiomyolipoma of the kidney. During the last decades, many efforts have been made to identify immunohistochemical markers to reach the right diagnosis. To date, staining for PAX8, cathepsin K, and melanogenesis markers are the most useful identifiers. However, the diagnosis requires the demonstration of the chromosomal rearrangement, and fluorescent in situ hybridization (FISH) is considered the gold standard. The outcome of Xp11 translocation renal cell carcinoma is highly variable, with some patients surviving decades with indolent disease and others dying rapidly of progressive disease. Despite most instances of t(6;11) renal cell carcinoma having an indolent clinical course, a few published cases demonstrate aggressive behavior. Recently, renal cell carcinomas with TFEB amplification have been described in connection with t(6;11) renal cell carcinoma. Those tumors appear to be associated with a more aggressive clinical course. For the aggressive cases of MiT family translocation carcinoma, the optimal therapy remains to be determined; however, new target therapies seem to be promising, and the search for predictive markers is mandatory.

Therapeutic Targeting of TFE3/IRS-1/PI3K/mTOR Axis in Translocation Renal Cell Carcinoma

PURPOSE

Translocation renal cell carcinoma (tRCC) represents a rare subtype of kidney cancer associated with various TFE3, TFEB, or MITF gene fusions that are not responsive to standard treatments for RCC. Therefore, the identification of new therapeutic targets represents an unmet need for this disease.

EXPERIMENTAL DESIGN

We have established and characterized a tRCC patient-derived xenograft, RP-R07, as a novel preclinical model for drug development by using next-generation sequencing and bioinformatics analysis. We then assessed the therapeutic potential of inhibiting the identified pathway using in vitro and in vivo models.

RESULTS

The presence of a SFPQ-TFE3 fusion [t(X;1) (p11.2; p34)] with chromosomal break-points was identified by RNA-seq and validated by RT-PCR. TFE3 chromatin immunoprecipitation followed by deep sequencing analysis indicated a strong enrichment for the PI3K/AKT/mTOR pathway. Consistently, miRNA microarray analysis also identified PI3K/AKT/mTOR as a highly enriched pathway in RP-R07. Upregulation of PI3/AKT/mTOR pathway in additional TFE3-tRCC models was confirmed by significantly higher expression of phospho-S6 (P < 0.0001) and phospho-4EBP1 (P < 0.0001) in established tRCC cell lines compared with clear cell RCC cells. Simultaneous vertical targeting of both PI3K/AKT and mTOR axis provided a greater antiproliferative effect both in vitro (P < 0.0001) and in vivo (P < 0.01) compared with single-node inhibition. Knockdown of TFE3 in RP-R07 resulted in decreased expression of IRS-1 and inhibited cell proliferation.

CONCLUSIONS

These results identify TFE3/IRS-1/PI3K/AKT/mTOR as a potential dysregulated pathway in TFE3-tRCC, and suggest a therapeutic potential of vertical inhibition of this axis by using a dual PI3K/mTOR inhibitor for patients with TFE3-tRCC.