Pattern multiplicity and fumarate hydratase (FH)/S-(2-succino)-cysteine (2SC) staining but not eosinophilic nucleoli with perinucleolar halos differentiate hereditary leiomyomatosis and renal cell carcinoma-associated renal cell carcinomas from kidney tumors without FH gene alteration

The Cytopathological Diagnosis of Fumarate Hydratase (FH)-Deficient Renal Cell Carcinoma in Two Patients With FH Gene Mutation

Fumarate hydratase-deficient renal cell carcinoma (FH-dRCC) is a high-grade renal cell carcinoma characterised by mutations in the FH gene. FH-dRCC is highly aggressive and has a poor prognosis, underscoring the importance of accurate diagnosis. Although the histopathological features of this neoplasm have been reported in previous studies, descriptions of its cytopathological features are limited. Here, we report the cytopathological morphologies of two cases of metastatic FH-dRCC in male patients aged 48 and 35 years. Case 1 presented with a cystic solid mass in the right retroperitoneal lumbar rib triangle region after the excision of a cystic tumour in the right kidney. Cytopathological examination of the fine-needle aspiration sample revealed papillary and tubular tumour cells. Case 2 developed abdominal ascites after bilateral nephrectomy, and cytopathological examination of ascitic fluid-characterised tumour cells with a high nuclear grade arranged in papillary and glandular patterns. In both cases, large tumour cells were observed with abundant eosinophilic cytoplasm, coarse chromatin and irregular nuclear shapes. Some cells exhibited characteristic eosinophilic macronucleoli and perinucleolar halos. Tumour cell clusters with a high nuclear grade, papillary structures, prominent eosinophilic macronucleoli and perinucleolar halos are the major cytopathological traits of FH-dRCC. CK7-negative/CA9-negative and PAX8-positive immunophenotypes may serve as important diagnostic markers. Moreover, the AKR1B10-positive/2SC-positive/FH-deficient immunophenotype contributes to the diagnosis of this tumour. Consequently, if the tumour cells have these characteristics, the diagnosis of FH-dRCC should be considered in cytology.

Clinicopathological and molecular features of so-called low-grade oncocytic fumarate hydratase-deficient renal cell carcinoma: a study of 5 cases

Low-grade oncocytic fumarate hydratase-deficient renal cell carcinoma (FHdRCC), resembling succinate dehydrogenase-deficient RCC morphologically, is a recently described uncommon variant of FHdRCC. We report five additional cases to enhance the understanding of this rare tumor type. These tumors had variably thick fibromuscular capsules with frequent intracapsular invasions and had prominently compact nests and/or tubules. The tumor cells were characterized by abundant dense eosinophilic cytoplasm imparting a ground glass-like appearance and by variable bubbly cytoplasm. Despite a predominantly low histology grade, focal nuclear pleomorphism was observed in two cases. Two cases showed FH negativity and 2SC positivity, while the remaining cases exhibited both FH and 2SC positivity. All cases were positive for PAX8, Vimentin, P504s, and SDHB, but negative for CD117, CA9, CK20, ALK, and cathepsin-K. CK7 and TFE3 positivity were seen in 2 and 4 of 5 cases, respectively. The whole exome sequencing and multiplex PCR-based next generation sequencing identified pathogenic or likely pathogenic FH mutations in three cases and failed in one case showing the FH-negative and 2SC-positive immunophenotype. The remaining case exhibiting both FH and 2SC positivity had a germline FH mutation of uncertain significance and single copy loss of chromosomes 1, 14, and 18. None of three cases who underwent FISH detections had TFE3 translocations. Follow-up time for the 5 cases ranged from 7 to 94 months (median 46 months; mean 52 months). All cases were alive without disease, except for case 4 being alive with a stable contralateral renal mass. While low-grade oncocytic FHdRCC has a relatively better prognosis than conventional FHdRCCs, further research is required to confirm this in the future.

Stimulator of interferon genes (STING) immunohistochemical expression in fumarate hydratase-deficient renal cell carcinoma: biological and potential predictive implications

Fumarate hydratase (FH)-deficient renal cell carcinoma is an aggressive neoplasm driven by inactivating mutations of the FH gene, which cause metabolites like S-(2-succinyl)cysteine (2SC) to accumulate and trigger cascades supporting malignant transformation. Although in preclinical models the c-GAS-STING pathway is activated by fumarate metabolites, its role in humans has not been explored yet. Eleven FH-deficient renal cell carcinomas, including primary neoplasms and metastases, were retrieved and evaluated for clinical-pathological features and immunohistochemical expression of FH, 2SC (commercially available), and STING. The in-house collection accounted for 0.2% of the 2011-2023 renal cell carcinomas cohort (5/2210). Eight-on-ten cases with available follow-up behaved aggressively (local recurrence/distant metastases). All tumors revealed FH staining loss and strong and diffuse 2SC immunolabeling. At least focal STING expression was detected in most primary tumors (9/11, 82%), often (78%) in a wide percentage of cells (≥ 30%). Notably, significant STING expression was observed in all but two aggressive renal neoplasms, with one of the remaining showing increased staining in its hepatic localization, and in 86% (6/7) of neoplasms significantly expressing PD-L1. In our series, (i) FH-deficient renal cell carcinoma represents 0.2% of in-house cases; (ii) combining FH loss and positive 2SC staining now commercially available is useful in primary and secondary tumors, supporting this latter marker's safe routine adoption; and (iii) a significant STING labeling (≥ 30%) in most of the samples, especially in those behaving aggressively and expressing PD-L1, provides novel insights regarding the molecular basis of FH-deficient renal cell carcinomas, proposing STING as a potential predictive marker.

Fumarate Hydratase-Deficient Renal Cell Carcinoma with Nucleolar Pattern of GATA3 Immunoexpression: Report of 2 Cases

Fumarate hydratase-deficient renal cell carcinoma (FH-deficient RCC) is a rare aggressive type of renal cell carcinoma. The significant morphologic overlap with other types of renal neoplasia and the limited availability of FH and 2-succinylcholine immunostains for diagnostic use outside large referral centers have created numerous diagnostic pitfalls. As FH-deficient RCC can be associated with hereditary leiomyomatosis and renal cell cancer syndrome, the importance of an accurate diagnosis goes beyond the prognosis and treatment of an individual patient. We present 2 patients with FH-deficient RCC showing a peculiar pattern of GATA3 immunoexpression restricted to tumor nucleoli. If confirmed in further larger studies, this could provide an additional diagnostic clue for considering the FH-deficient RCC diagnosis, and given the frequent papillary morphology and possible hilar location can lead to the misdiagnosis as high-grade urothelial carcinoma, and is an important diagnostic pitfall to be aware of.

A rare case of FH-deficient renal cell carcinoma with signet ring cells features

Fumarate hydratase-deficient renal cell carcinoma (FH-deficient RCC) is a clinically aggressive tumor with high rates of progression and mortality. A wide range of morphological variations has been observed in FH-deficient RCC, initially described as type 2 papillary RCC or unclassified RCC. Here, we report a case of FH-deficient RCC with rare signet ring cells features. The patient was diagnosed with FH-deficient renal cell carcinoma and suspected to have hereditary leiomyomatosis and renal cell cancer (HLRCC) syndrome. After 4 months, pulmonary metastasis occurred in the patient. We herein describe the first case of FH-deficient renal tumor with signet ring cells features, which expands the morphological spectrum of this tumor. More importantly, this variant can be a diagnostic pitfall, we emphasize that pathologists should consider not only the diagnosis of metastatic signet ring cell carcinoma and ALK rearrangement renal cell carcinoma but also FH-deficient renal cell carcinoma.

Fumarate Hydratase-Deficient Renal Cell Carcinoma With Predominant Tubulocystic Features Mimics Tubulocystic Renal Cell Carcinoma

CONTEXT.—

Fumarate hydratase (FH)-deficient renal cell carcinoma (RCC) rarely exhibits a predominant tubulocystic architecture with few other components. RCC with pure tubules and cysts lined by eosinophilic tumor cells with prominent nucleoli would raise the diagnosis of tubulocystic RCC. It is important to differentiate the 2 entities because they lead to different outcomes.

OBJECTIVE.—

To address this concern, a multicenter study was implemented to explore useful clinicopathologic features in differentiation between tubulocystic FH-deficient RCC and tubulocystic RCC.

DESIGN.—

Clinical factors included age, sex, tumor size, and outcome. Morphologic factors included cell morphology, presence or absence of a nontubulocystic component, and stromal findings. Immunohistochemistry, fluorescence in situ hybridization, and next-generation sequencing were performed to explore the protein expression and molecular profiles of the 2 entities.

RESULTS.—

We evaluated 6 patients with tubulocystic RCC and 10 patients with tubulocystic FH-deficient RCC. Tubulocystic RCC exhibited a small size (<4.0 cm, pT1a), low Ki-67 index (<5%), retained FH, and negative 2SC expression. Tubulocystic FH-deficient RCC had a relatively large size and a high Ki-67 index. Perinucleolar haloes, loss of FH, and 2SC positivity were always observed. Pure tubulocystic architecture was not observed in FH-deficient RCC, because focal nontubulocystic components can always be seen.

CONCLUSIONS.—

We emphasized multiple sectioning to identify a nontubulocystic architecture to exclude tubulocystic RCC. Moreover, tumor size, FH/2SC staining, and the Ki-67 index can differentiate tubulocystic FH-deficient RCC from tubulocystic RCC. The diagnosis of tubulocystic RCC was not recommended in renal mass biopsy because of the limited tissues sampled.

Comparison of Primary and Metastatic Fumarate Hydratase-Deficient Renal Cell Carcinomas Documents Morphologic Divergence and Potential Diagnostic Pitfall With Peritoneal Mesothelioma

Fumarate hydratase (FH)-deficient renal cell carcinomas are rare neoplasms characterized by wide morphologic heterogeneity and pathogenetic mutations in the FH gene. They often show aggressive behavior with rapid diffusion to distant organs, so novel therapeutic scenarios have been explored, including EGFR inhibitors and PD-L1 expression for targeted immunotherapy. Herein, we investigated a series of 11 primary FH-deficient renal cell carcinomas and 7 distant metastases to evaluate tumor heterogeneity even in metastatic sites and estimate the specific spread rates to various organs. Furthermore, the tumors were tested for immunohistochemical PD-L1 expression and EGFR mutations. Most metastatic cases involved the abdominal lymph nodes (4/7; 57%), followed by the peritoneum (3/7; 42%), the liver (2/7; 29%), and the lungs (1/7; 14%). Six metastatic localizations were histologically documented, revealing a morphologic heterogeneous architecture often differing from that of the corresponding primary renal tumor. Peritoneal involvement morphologically resembled a benign reactive mesothelial process or primary peritoneal mesothelioma, thus advocating to perform an accurate immunohistochemical panel, including PAX8 and FH, to reach a proper diagnosis. A pure low-grade succinate dehydrogenase-looking primary FH-deficient renal cell carcinoma was also recorded. As for therapy, significant PD-L1 labeling was found in 60% of primary renal tumors, whereas none of them carried pathogenetic EGFR mutations. Our data show that FH-deficient renal cell carcinoma may be morphologically heterogeneous in metastases as well, which involve the lymph nodes, the liver, and the peritoneum more frequently than other renal tumors. Due to the high frequency of this latter (42%), pathologists should always be concerned about ruling out mesothelial-derived mimickers, and the occurrence of rarer, primary, low-grade-looking types. Finally, contrary to EGFR mutations, PD-L1 expression could be a possible predictive biomarker for the therapy of these tumors.

[2022 WHO classification of renal cell carcinomas: Focus on papillary renal cell carcinoma]

Renal cell carcinomas (RCC) represent a group of heterogeneous tumors whose classification has greatly evolved since 1981. The latest update in 2022 classifies all renal cell carcinomas into six categories according to their morphology or the detection of specific molecular alterations. Molecular disassembly of renal cell carcinomas with papillary features has enabled the identification of new entities characterized by a specific molecular alteration, such as Fumarate Hydratase (FH) deficient RCC, TFE3-rearranged RCC or TFEB-altered RCC. This new classification allows for a more accurate diagnosis but requires a thorough knowledge of the genomic alterations to search for with immunohistochemical or molecular biology techniques. According to the new WHO 2022 classification, papillary renal cell carcinoma (PRC) type 1 or type 2 classification is no longer recommended. A classification based on nucleolar ISUP grade must be preferred: low-grade PRC (ISUP 1-2) or high-grade PRC (ISUP 3-4). The other prognostic factors remain the same: the pTNM stage, lymphovascular invasion, and the presence or absence of dedifferentiated areas referring to sarcomatoid or rhabdoid features. Of note, the presence of necrosis is not currently recognized as a poor prognostic element for this type of carcinoma. The diagnosis of high-grade PRC is from now on a diagnosis of exclusion. It can only be sustained after having ruled out TFE3-rearranged RCC, TFEB-altered RCC, and FH-deficient RCC. For clinicians, the diagnosis of PRC implies suggesting an oncogenetic consultation to screen for an associated genetic tumor syndrome regardless of the patient's age.

Contemporary review of papillary renal cell carcinoma-current state and future directions

Historically, papillary renal cell carcinoma (PRCC) was divided into two types, type 1 and type 2, based solely on morphology. However, it is apparent that PRCC is far more complex and represents a histological, clinical, and molecular spectrum. There has been a significant evolution in our understanding of PRCC, highlighted by the recognition of new and molecularly defined entities that were previously included in PRCC type 2. This contemporary review addresses the evolving concepts regarding the PRCC, including why it is no longer needed to subtype PRCC, the current molecular landscape, prognostic parameters, and PRCC variants, including biphasic PRCC, papillary renal neoplasm with reverse polarity, and Warthin-like PRCC. Pathologists should also be aware of the potential mimickers of both low-grade and high-grade PRCCs as well as some new and emerging entities that may show papillary growth that should be excluded in the diagnostic workup. The evolving knowledge of PRCC biomarkers, morphologic patterns, and PRCC variants could also have important implications for clinical management. Lastly, the heterogeneity within the PRCC spectrum needs to be further studied, aiming to better stratify PRCC for appropriate clinical management and systemic therapy.

Fumarate hydratase-deficient renal cell carcinoma: an oncology care institutional experience

Renal cell carcinoma (RCC) accounts for 2% of all cancer cases worldwide, and majority are sporadic. The latest World Health Organization (WHO) classification of renal cell tumors (fifth edition, 2022) has molecularly defined renal tumor entities, which includes fumarate hydratase (FH)-deficient RCC. FH-deficient RCC is an aggressive carcinoma caused by pathogenic alterations in FH gene, seen in 15% of patients with hereditary leiomyomatosis and renal cell cancer syndrome (HLRCC) syndrome. These tumors occur more frequently at a younger age and present at an advanced stage, carrying a dismal prognosis. We report a series of 10 cases of FH-deficient RCC. The mean age was 49.8 years, and all cases presented in advanced stages (III and IV). Morphologically, the cases had varied architectural patterns with characteristic eosinophilic macronucleoli and perinucleolar halo. On immunohistochemistry (IHC), all showed diffuse nucleo-cytoplasmic expression of S-(2-succino)-cysteine (2-SC), with loss of FH in seven cases. FH-deficient RCCs are aggressive neoplasms and can be diagnosed using specific IHC markers (FH and 2-SC). These patients should undergo germline testing for FH gene mutation, genetic counseling, and surveillance of family members.

The New WHO Category of "Molecularly Defined Renal Carcinomas": Clinical and Diagnostic Features and Management Implications

The evolution of classification of renal tumors has been impacted since the turn of the millennium by rapid progress in histopathology, immunohistochemistry, and molecular genetics. Together, these features have enabled firm recognition of specific, classic types of renal cell carcinomas, such as clear cell renal cell carcinoma, that in current practice trigger histologic-type specific management and treatment protocols. Now, the fifth Edition World Health Classification's new category of "Molecularly defined renal carcinomas" changes the paradigm, defining a total of seven entities based specifically on their fundamental molecular underpinnings. These tumors, which include TFE3-rearranged, TFEB-altered, ELOC-mutated, fumarate hydratase-deficient, succinate dehydrogenase-deficient, ALK-rearranged, and SMARCB1-deficient renal medullary carcinoma, encompass a wide clinical and histopathologic phenotypic spectrum of tumors. Already, important management aspects are apparent for several of these entities, while emerging therapeutic angles are coming into view. A brief, clinically-oriented introduction of the entities in this new category, focusing on relevant diagnostic, molecular, and management aspects, is the subject of this review.

Sarcomatoid and Rhabdoid Renal Cell Carcinoma: Clinical, Pathologic, and Molecular Genetic Features

Renal cell carcinoma (RCC) with sarcomatoid and rhabdoid morphologies has an aggressive biological behavior and a typically poor prognosis. The current 2022 WHO classification of renal tumors does not include them as distinct histologic entities but rather as transformational changes that may arise in a background of various distinct histologic types of RCC. The sarcomatoid component shows malignant spindle cells that may grow as intersecting fascicles, which is reminiscent of pleomorphic undifferentiated sarcoma. The rhabdoid cells are epithelioid cells with eccentrically located vesicular nuclei with prominent nucleoli and large intracytoplasmic eosinophilic inclusions. Studies have shown that RCCs with sarcomatoid and rhabdoid differentiation have distinctive molecular features. Sarcomatoid RCC harbors shared genomic alterations in carcinomatous and rhabdoid components, but also enrichment of specific genomic alterations in the sarcomatoid element, suggesting molecular pathways for development of sarcomatoid growth from a common clonal ancestor. Rhabdoid differentiation also arises through clonal evolution although less is known of specific genomic alterations in rhabdoid cells. Historically, treatment has lacked efficacy, although recently immunotherapy with PD-1/PD-L1/CTLA-4 inhibitors has produced significant clinical responses. Reporting of sarcomatoid and rhabdoid features in renal cell carcinoma is required by the College of American Pathologists and the International Collaboration on Cancer Reporting. This manuscript reviews the clinical, pathologic, and molecular features of sarcomatoid RCC and rhabdoid RCC with emphasis on the morphologic features of these tumors, significance of diagnostic recognition, the molecular mechanisms of tumorigenesis and differentiation along sarcomatoid and rhabdoid lines, and advances in treatment, particularly immunotherapy.

Case report: successful response to bevacizumab combined with erlotinib for a novel FH gene mutation hereditary leiomyoma and renal cell carcinoma

FH-deficient Renal Cell Carcinoma (FH-deficient RCC) are inherited tumors caused by mutations in the fumarate hydratase (FH) gene, which plays a role in the tricarboxylic acid cycle. These mutations often result in aggressive forms of renal cell carcinoma (RCC) and other tumors. Here, we present a case of FH-deficient RCC in a 43-year-old woman with a history of uterine fibroids. She exhibited a new heterozygous mutation in exon six of the FH gene (c.799_803del, c.781_796del). The patient had multiple bone metastases and small subcutaneous nodules in various areas such as the shoulders, back, and buttocks. Biopsy of a subcutaneous nodule on the right side revealed positive expression of 2-succinate-cysteine (2SC), and FH staining indicated FH expression deletion. The patient underwent treatment with a combination of erlotinib and bevacizumab, which resulted in significant efficacy with moderate side effects. This treatment combination may be recommended as a standard regimen. This case underscores the importance of genetic testing in patients with advanced renal cancer to enhance diagnostic accuracy. Furthermore, it provides insights into potential treatment approaches for FH-deficient RCC.

Memory/Active T-Cell Activation Is Associated with Immunotherapeutic Response in Fumarate Hydratase-Deficient Renal Cell Carcinoma

PURPOSE

Fumarate hydratase-deficient renal cell carcinoma (FH-deficient RCC) is a rare and lethal subtype of kidney cancer. However, the optimal treatments and molecular correlates of benefits for FH-deficient RCC are currently lacking.

EXPERIMENTAL DESIGN

A total of 91 patients with FH-deficient RCC from 15 medical centers between 2009 and 2022 were enrolled in this study. Genomic and bulk RNA-sequencing (RNA-seq) were performed on 88 and 45 untreated FH-deficient RCCs, respectively. Single-cell RNA-seq was performed to identify biomarkers for treatment response. Main outcomes included disease-free survival (DFS) for localized patients, objective response rate (ORR), progression-free survival (PFS), and overall survival (OS) for patients with metastasis.

RESULTS

In the localized setting, we found that a cell-cycle progression signature enabled to predict disease progression. In the metastatic setting, first-line immune checkpoint inhibitor plus tyrosine kinase inhibitor (ICI+TKI) combination therapy showed satisfactory safety and was associated with a higher ORR (43.2% vs. 5.6%), apparently superior PFS (median PFS, 17.3 vs. 9.6 months, P = 0.016) and OS (median OS, not reached vs. 25.7 months, P = 0.005) over TKI monotherapy. Bulk and single-cell RNA-seq data revealed an enrichment of memory and effect T cells in responders to ICI plus TKI combination therapy. Furthermore, we identified a signature of memory and effect T cells that was associated with the effectiveness of ICI plus TKI combination therapy.

CONCLUSIONS

ICI plus TKI combination therapy may represent a promising treatment option for metastatic FH-deficient RCC. A memory/active T-cell-derived signature is associated with the efficacy of ICI+TKI but necessitates further validation.

Update on Selected High-grade Renal Cell Carcinomas of the Kidney: FH-deficient, ALK-rearranged, and Medullary Carcinomas

High-grade renal cell carcinoma (RCC), often diagnosed at advanced stages, significantly contributes to renal cancer-related mortality. This review explores the progress in understanding specific subtypes of high-grade RCC, namely fumarate hydratase (FH)-deficient RCC, anaplastic lymphoma kinase (ALK)-rearranged RCC, and SMARCB1-deficient renal medullary carcinoma, all of which are now recognized as molecularly defined entities in the WHO classification system (2022). While these entities each exhibit a morphologic spectrum that overlaps with other high-grade RCC, ancillary tools developed based on their distinctive molecular alterations can help establish a specific diagnosis, underscoring the importance of integrating molecular findings into diagnostic paradigms. It is important to exclude these specific tumor types in cases with similar morphologic spectrum before rendering a diagnosis of high-grade papillary RCC, collecting duct carcinoma, or RCC, NOS. Several gray areas exist within the spectrum of high-grade uncommon types of RCC, necessitating continued research to enhance diagnostic precision and therapeutic options.

The clinicopathologic and molecular features, and treatment outcome of fumarate hydratase-deficient renal cell carcinoma: a retrospective comparison with type 2 papillary renal cell carcinoma

BACKGROUND

To compare clinicopathologic, molecular features, and treatment outcome between fumarate hydratase-deficient renal cell carcinoma (FH-dRCC) and type 2 papillary renal cell carcinoma (T2 pRCC).

METHODS

Data of T2 pRCC patients and FH-dRCC patients with additional next-generation sequencing information were retrospectively analyzed. The cancer-specific survival (CSS) and disease-free survival (DFS) were primary endpoint.

RESULTS

A combination of FH and 2-succino-cysteine (2-SC) increased the rate of negative predictive value of FH-dRCC. Compared with T2 pRCC cases, FH-dRCC cases displayed a greater prevalence in young patients, a higher frequency of radical nephrectomy. Seven FH-dRCC and two T2 pRCC cases received systemic therapy. The VEGF treatment was prescribed most frequently, with an objective response rate (ORR) of 22.2% and a disease control rate (DCR) of 30%. A combined therapy with VEGF and checkpoint inhibitor reported an ORR of 40% and a DCR of 100%. FH-dRCC cases showed a shortened CSS (P = 0.042) and DFS (P < 0.001). The genomic sequencing revealed 9 novel mutations.

CONCLUSIONS

Coupled with genetic detection, immunohistochemical biomarkers (FH and 2-SC) can distinguish the aggressive FH-dRCC from T2 pRCC. Future research is awaited to illuminate the association between the novel mutations and the clinical phenotypes of FH-dRCC in the disease progression.

The Application and Pitfalls of Immunohistochemical Markers in Challenging Diagnosis of Genitourinary Pathology

CONTEXT.—

The morphologic features of different entities in genitourinary pathology overlap, presenting a diagnostic challenge, especially when diagnostic materials are limited. Immunohistochemical markers are valuable when morphologic features alone are insufficient for definitive diagnosis. The World Health Organization classification of urinary and male genital tumors has been updated for 2022. An updated review of immunohistochemical markers for newly classified genitourinary neoplasms and their differential diagnosis is needed.

OBJECTIVE.—

To review immunohistochemical markers used in the diagnosis of genitourinary lesions in the kidney, bladder, prostate, and testis. We particularly emphasized difficult differential diagnosis and pitfalls in immunohistochemistry application and interpretation. New markers and new entities in the 2022 World Health Organization classifications of genitourinary tumors are reviewed. Recommended staining panels for commonly encountered difficult differential diagnoses and potential pitfalls are discussed.

DATA SOURCES.—

Review of current literature and our own experience.

CONCLUSIONS.—

Immunohistochemistry is a valuable tool in the diagnosis of problematic lesions of the genitourinary tract. However, the immunostains must be carefully interpreted in the context of morphologic findings with a thorough knowledge of pitfalls and limitations.

AKR1B10 Is a New Sensitive and Specific Marker for Fumarate Hydratase-Deficient Renal Cell Carcinoma

Fumarate hydratase (FH)-deficient renal cell carcinoma (RCC) is a rare and distinct subtype of renal cancer caused by FH gene mutations. FH negativity and s-2-succinocysteine (2SC) positivity on immunohistochemistry can be used to screen for FH-deficient RCC, but their sensitivity and specificity are not perfect. The expression of AKR1B10, an aldo-keto reductase that catalyzes cofactor-dependent oxidation-reduction reactions, in RCC is unclear. We compared AKR1B10, 2SC, and FH as diagnostic biomarkers for FH-deficient RCC. We included genetically confirmed FH-deficient RCCs (n = 58), genetically confirmed TFE3 translocation RCCs (TFE3-tRCC) (n = 83), clear cell RCCs (n = 188), chromophobe RCCs (n = 128), and papillary RCCs (pRCC) (n = 97). AKR1B10, 2SC, and FH were informative diagnostic markers. AKR1B10 had 100% sensitivity and 91.4% specificity for FH-deficient RCC. The nonspecificity of AKR1B10 was shown in 26.5% of TFE3-tRCCs and 21.6% of pRCCs. 2SC showed 100% sensitivity and 88.9% specificity. However, nonspecificity for 2SC was evident in multiple RCCs, including pRCC, TFE3-tRCC, clear cell RCCs, and chromophobe RCCs. FH was 100% specific but 84.5% sensitive. AKR1B10 served as a highly sensitive and specific diagnostic biomarker. Our findings suggest the value of combining AKR1B10 and 2SC to screen for FH-deficient RCC. AKR1B10+/2SC+/FH- cases can be diagnosed as FH-deficient RCC. Patients with AKR1B10+/2SC+/FH+ are highly suspicious of FH-deficient RCC and should be referred for FH genetic tests.

[FH (Fumarate Hydratase)-deficient renal cell carcinoma: A case report]

Fumarate hydratase deficient renal cell carcinoma (FH-RCC) is a rare malignant neoplasia caused by constitutive or somatic mutations in the FH gene whose diagnosis is primordial, requiring genetic counselling. Because of histological heterogeneity, such tumors have been in the past misclassified as "type 2 papillary carcinoma", "tubulo-cystic renal cell carcinoma" or "high grade papillary carcinoma". We report here a case of FH deficient renal cell carcinoma (FH-RCC) in a 69years old patient. Through this observation, we precise the epidemiological and histological aspects and diagnosis criteria of this rare tumor.

Clinical Characteristics of Molecularly Defined Renal Cell Carcinomas

Kidney tumors comprise a broad spectrum of different histopathological entities, with more than 0.4 million newly diagnosed cases each year, mostly in middle-aged and older men. Based on the description of the 2022 World Health Organization (WHO) classification of renal cell carcinoma (RCC), some new categories of tumor types have been added according to their specific molecular typing. However, studies on these types of RCC are still superficial, many types of these RCC currently lack accurate diagnostic standards in the clinic, and treatment protocols are largely consistent with the treatment guidelines for clear cell RCC (ccRCC), which might result in worse treatment outcomes for patients with these types of molecularly defined RCC. In this article, we conduct a narrative review of the literature published in the last 15 years on molecularly defined RCC. The purpose of this review is to summarize the clinical features and the current status of research on the detection and treatment of molecularly defined RCC.

Clinico-pathological implications of the 2022 WHO Renal Cell Carcinoma classification

The new WHO classification of urogenital tumours published in 2022, contains significant revisions upon the previous 2016 version regarding Renal Cell Carcinoma (RCC). While the most common histotype remains almost untouched, some of the main novelties concerns papillary RCC and oncocytic neoplasms. The main change is the introduction of a new category of molecularly-defined RCC, which includes TFE3-rearranged RCC, TFEB-rearranged, and TFEB-amplified RCC, FH-deficient RCC, SDH-deficient RCC, ALK-rearranged RCC, ELOC (formerly TCEB1)-mutated RCC, SMARCB1 (INI1)-deficient RCC. In this paper we analyze the current knowledge on emerging entities and molecularly-defined RCC to assess whether the current pathological classification offers the oncologist the possibility of selecting more specific and personalized treatments, from both those currently available, as well as those that will soon be available.

Fumarate Hydratase and S-(2-Succinyl)-Cysteine Immunohistochemistry Shows Evidence of Fumarate Hydratase Deficiency in 2% of Uterine Leiomyosarcomas: A Cohort Study of 348 Tumors

Approximately 1% to 1.5% of uterine leiomyomas are fumarate hydratase (FH)-deficient (FHd). A subset of these are associated with germline FH mutations. However, the prevalence and clinicopathologic characteristics of FHd uterine leiomyosarcoma (uLMS) remain unknown. Clinicopathologic data were collected for 348 uLMS. Morphologic features associated with FH deficiency (staghorn-type vessels, alveolar-pattern edema, macronucleoli with perinucleolar clearing, eosinophilic cytoplasmic inclusions, and chain-like nuclear arrangement) were documented. All 348 tumors were studied by FH immunohistochemistry. Eighty-nine were also studied by S-(2-succinyl)-cysteine (2SC) immunohistochemistry. Seven (2%) FHd uLMS were identified. Five showed uniformly negative FH and diffusely positive 2SC immunostaining; 1 showed variably negative to weak to strong FH and diffusely positive 2SC immunostaining; and 1 showed retained FH staining alongside positive 2SC confined to a morphologically distinct subclone. Three of 7 patients had extrauterine disease at presentation, and 3 of 6 had persistent disease or died from disease. Macronucleoli with perinucleolar clearing were significantly more common in FHd uLMS (7/7) than in uLMS with retained FH (182/341; P =0.017). Disease-specific survival, disease-free survival, and other morphologic features of FH deficiency did not differ significantly between FHd and FH-retained tumors. Our data emphasize that immunohistochemical FH deficiency does not preclude malignancy in uterine smooth muscle tumors. However, the biological significance and molecular basis of FH deficiency in uLMS, including any relationship to germline FH mutation, remain unknown, and a larger multi-institutional effort is necessary to gather sufficient FHd uLMS for more robustly powered clinicopathologic and for molecular characterization.

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.

Morphologic Characteristics and Mutational Analysis of Fumarate Hydratase Deficient Kidney and Smooth Muscle Tumors

OBJECTIVES

Fumarate hydratase (FH)-deficient tumors can occur due to germline or somatic mutations and have distinctive morphologic features. The aims of this study are to refine morphologic criteria and identify mutations in FH-deficient smooth muscle tumors (SMTs).

METHODS

The morphology of SMTs and kidney tumors submitted to a national reference laboratory for FH immunohistochemistry (IHC) was reviewed by two gynecologic and two genitourinary pathologists, respectively. Fisher exact test was used for analysis. Fourteen SMTs were sequenced using the Illumina TruSight Oncology 500 Assay.

RESULTS

Twenty-two kidney tumors (5 FH deficient) and 51 SMTs (27 FH deficient) were reviewed. FH-deficient kidney tumors exclusively showed cord-like growth, rhabdoid change, and absence of coagulative tumor necrosis and psammoma bodies. FH-deficient SMTs were significantly more likely to have staghorn vessels, eosinophilic cytoplasmic inclusions, schwannoma-like areas, or hereditary leiomyomatosis and renal cell cancer-like nuclei (P < .05 for each). Seven of 14 sequenced SMTs showed mutations of the FH gene and no other driver mutations.

CONCLUSIONS

FH-deficient SMTs submitted for FH immunohistochemistry (IHC) showed distinct morphology. Although FH IHC is used for screening of FH-deficient tumors, FH mutations were identified in only 50% of FH-deficient SMTs. This highlights the need for additional exploration of mechanisms of FH protein loss in tumors lacking FH mutations.

Characterization of protein S-(2-succino)-cysteine (2SC) succination as a biomarker for fumarate hydratase-deficient renal cell carcinoma

Fumarate hydratase (FH)-deficient renal cell carcinoma (RCC) is an aggressive, rare genetic disease affecting the kidney and other organ systems. We constructed a specialized multi-institutional cohort of 20 primary FH-deficient RCC cases with aims of characterizing a new commercially available antibody, S-(2-succino)-cysteine (2SC). Herein, we present our findings on the biomarker characterization and performance of 2SC expression by immunohistochemistry (IHC) in FH-deficient RCC and other common and rare RCC subtypes. Morphological assessment revealed characteristic cytomorphologic features and a majority (55%) of FH-deficient RCC had mixed architectural growth patterns. We observed predominantly diffuse and strong cytoplasmic staining with limited nuclear positivity for 2SC staining on IHC. Receiver operating characteristic curves (ROC) for 2SC identified the threshold IHC score (cutoff) as 90, with the sensitivity and specificity being 100% and 91%, respectively. The findings of the present study along with the prior evidence in literature encourage utilization of 2SC as a positive marker along with the loss of FH expression by anti-FH IHC staining as a negative marker, in clinical and/or pathologic scenarios when considering FH-deficient RCC in the differential diagnosis. FH^-/2SC⁺ may serve as a comprehensive IHC panel in identifying such cases and excluding morphologically similar entities.

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.

Identification of a S-(2-succino)cysteine breakdown pathway that uses a novel S-(2-succino) lyase

Succination is the spontaneous reaction between the respiratory intermediate fumarate and cellular thiols that forms stable S-(2-succino)-adducts such as S-(2-succino)cysteine (2SC). 2SC is a biomarker for conditions associated with elevated fumarate levels, including diabetes, obesity, and certain cancers, and succination likely contributes to disease progression. Bacillus subtilis has a yxe operon-encoded breakdown pathway for 2SC that involves three distinct enzymatic conversions. The first step is N-acetylation of 2SC by YxeL to form N-acetyl-2SC (2SNAC). YxeK catalyzes the oxygenation of 2SNAC, resulting in its breakdown to oxaloacetate and N-acetylcysteine, which is deacetylated by YxeP to give cysteine. The monooxygenase YxeK is key to the pathway but is rare, with close homologs occurring infrequently in prokaryote and fungal genomes. The existence of additional 2SC breakdown pathways was not known prior to this study. Here, we used comparative genomics to identify a S-(2-succino) lyase (2SL) that replaces yxeK in some yxe gene clusters. 2SL genes from Enterococcus italicus and Dickeya dadantii complement B. subtilis yxeK mutants. We also determined that recombinant 2SL enzymes efficiently break down 2SNAC into fumarate and N-acetylcysteine, can perform the reverse reaction, and have minor activity against 2SC and other small molecule thiols. The strong preferences both YxeK and 2SL enzymes have for 2SNAC indicate that 2SC acetylation is a conserved breakdown step. The identification of a second naturally occurring 2SC breakdown pathway underscores the importance of 2SC catabolism and defines a general strategy for 2SC breakdown involving acetylation, breakdown, and deacetylation.

WHO 2022 landscape of papillary and chromophobe renal cell carcinoma

The 5th edition of the WHO Classification of Tumours of the Urinary and Male Genital Systems contains relevant revisions and introduces a group of molecularly defined renal tumour subtypes. Herein we present the World Health Organization (WHO) 2022 perspectives on papillary and chromophobe renal cell carcinoma with emphasis on their evolving classification, differential diagnosis, and emerging entities. The WHO 2022 classification eliminated the type 1/2 papillary renal cell carcinoma (pRCC) subcategorization, given the recognition of frequent mixed tumour phenotypes and the existence of entities with a different molecular background within the type 2 pRCC category. Additionally, emerging entities such as biphasic squamoid alveolar RCC, biphasic hyalinising psammomatous RCC, papillary renal neoplasm with reverse polarity, and Warthin-like pRCC are included as part of the pRCC spectrum, while additional morphological and molecular data are being gathered. In addition to oncocytomas and chromophobe renal cell carcinoma (chRCC), a category of 'other oncocytic tumours' with oncocytoma/chRCC-like features has been introduced, including emerging entities, most with TSC/mTOR pathway alterations (eosinophilic vacuolated tumour and so-called 'low-grade' oncocytic tumour), deserving additional research. Eosinophilic solid and cystic RCC was accepted as a new and independent tumour entity. Finally, a highly reproducible and clinically relevant universal grading system for chRCC is still missing and is another niche of ongoing investigation. This review discusses these developments and highlights emerging morphological and molecular data relevant for the classification of renal cell carcinoma.

GATA3 aids in distinguishing fumarate hydratase-deficient renal cell carcinoma from papillary renal cell carcinoma

GATA3 has been reported to be positive in clear cell papillary renal cell carcinoma and papillary renal neoplasm with reverse polarity. However, its features in high-grade RCC remain unclear. Despite the emergence of novel renal entities, FH-deficient RCC remains one of the most aggressive renal neoplasms. The diagnosis is mainly based on the loss of FH at the protein level. Previous studies have shown that inclusion-like nuclei, multiple architectural patterns, FH loss, and 2SC positivity can differentiate FH-deficient RCC from other RCC. In some FH-deficient RCC cases, FH is normally expressed and is difficult to diagnose. This study included 11 FH-deficient RCC, and GATA3 showed different expression in seven cases. However, 147 papillary renal cell carcinomas were included, and GATA3 expression was negative. A comparison of clinicopathological aspects between 11 FH-deficient RCC and 30 high-grade PRCC showed statistical significance in age, size, multiple architectural patterns, inclusion-like nuclei, and prognosis. However, PRCC exhibited similar characteristics. CK7, GATA3, and FH profiles were also statistically significant. Different chromosomal alterations were found in FH-deficient RCC, and chromosomal alterations were not different between FH-deficient RCC and PRCC. GATA3 was positive in 33 % (7/21) of collecting duct carcinomas and negative in other high-grade renal neoplasms. GATA3 is negative in PRCC, but can be positive in FH-deficient RCC and collecting duct carcinoma. GATA3 expression may indicate a worse outcome in high-grade RCC with papillary architecture. We recommend GATA3 IHC for the differential diagnosis and prognostic assessment of high-grade RCC with papillary architecture.

Clinicopathological and molecular characteristics of fumarate-hydratase-deficient uterine smooth muscle tumors: A single-center study of 52 cases

AIMS

The fumarate hydratase (FH) gene germline mutations cause hereditary leiomyomatosis and renal cell carcinoma syndrome (HLRCC), predisposing carriers to uterine and cutaneous leiomyomas and renal cell carcinoma (RCC). In this study, we aim to investigate morphology and the correlation between FH mutation in FH-deficient (FH-d) uterine smooth muscle tumors (uSMTs).

METHODS AND RESULTS

We conducted immunohistochemical staining in 161 cases of uSMTs to detect FH deficiency. We identified 52 (52/161, 32%) cases of FH-d, including 34 leiomyomas with bizarre nuclei, 10 uSMTs of uncertain malignant potential (STUMPs), 4 cellular leiomyomas, 3 usual type leiomyomas, and 1 leiomyosarcoma. Patients with FH-d were aged 24-67 years (median, 40 years). The most common FH-d morphological features included staghorn-shaped blood vessels (87%), bizarre nuclei (81%), alveolar pattern edema (65%), macronucleoli surrounded by a halo (65%), cytoplasmic eosinophilic globules (56%), and chain-like distribution of smooth muscle cells (52%). A targeted next generation sequence was performed in 11 of 52 FH-d tumors. Five (5/11, 45%) cases were found with FH germline mutations, including four leiomyomas with bizarre nuclei and one STUMP. The median age of patients with germline FH mutation was 30 years. The germline mutations including three pathogenic, one likely pathogenic, and one rare uncertain clinical significance variants.

CONCLUSIONS

Our results revealed that FH-d uSMTs usually exhibit the distinct morphology features and high frequency of FH germline mutations. The combination of predictive morphology evaluation, FH immunotype and molecular testing is helpful for the screening of HLRCC in uSMTs.

Renal cell carcinoma in children and adolescents: A retrospective study of a French-Italian series of 93 cases

BACKGROUND

Renal cell carcinomas represent 2 to 5% of kidney malignancies in children and adolescents. Appropriate diagnostic and classification are crucial for the correct management of the patients and in order to avoid inappropriate preoperative chemotherapy, which is usually recommended if a Wilms tumor is suspected.

METHODS

a French-Italian series of 93 renal cell carcinomas collected from 1990 to 2019 in patients aged less than 18 years old was reclassified according to the 2016 WHO classification and the latest literature. TFE3 and TFEB FISH analyses and a panel of immunohistochemical stains were applied.

RESULTS

The median age at diagnosis was 11 years (range: 9 months - 17 years). MiT family (MiTF) translocation renal cell carcinomas accounted for 52% of the tumors, followed by papillary renal cell carcinomas (20%) and unclassified renal cell carcinomas (13%). Other subtypes, such as SDHB-deficient and Fumarate hydratase-deficient renal cell carcinomas, represented 1 to 3% of the cases. We also described a case of ALK-rearranged renal cell carcinoma with a metanephric adenoma-like morphology.

CONCLUSION

A precise histological diagnosis is mandatory as targeted therapy could be applied for some RCC subtypes, i.e., MiTF-translocation and ALK-translocation renal cell carcinomas. Moreover, some RCC subtypes may be associated with a predisposition syndrome that will impact patients' and family's management and genetic counseling. A precise RCC subtype is also mandatory for the clinical management of the patients and the inclusion in new prospective clinical trials.

What's new in the WHO 2022 classification of kidney tumours?

The World Health Organization (WHO) 2022 classification of urinary and male genital tumours (5th edition) has significantly improved our understanding of the morphologic, immunohistochemical, and molecular characteristics of renal tumours. The aim of this review is to outline the most important changes and diagnostic updates in the WHO 2022 classification of kidney tumours. A major change in this edition is the grouping of renal tumours into broader categories that include "clear cell renal tumours", "papillary renal tumours", "oncocytic and chromophobe renal tumours", "collecting duct tumours" as well as adding two categories of "other renal tumours" and "molecularly defined renal carcinomas". Novel entities included in the WHO 2022 classification are eosinophilic solid and cystic renal cell carcinoma (ESC RCC), anaplastic lymphoma kinase (ALK)-rearranged RCC and ELOC (formerly TCEB1)-mutated RCC. The category of "other renal tumours" includes a group of diverse, unrelated renal tumours that do not fit into other categories. The group of "molecularly defined renal carcinomas" reflects recent discoveries in the renal tumour genomics. These molecularly-defined renal entities demonstrate a set of morphologic features reflecting genotype-phenotype relationships. Final diagnosis of such entities rests on phenotypic and immunohistochemical (IHC) correlation, usually associated with IHC surrogate makers that reflect specific genetic abnormalities.

Common Diagnostic Challenges and Pitfalls in Genitourinary Organs, With Emphasis on Immunohistochemical and Molecular Updates

CONTEXT.—

Lesions in the genitourinary (GU) organs, both benign and malignant, can demonstrate overlapping morphology, and practicing surgical pathologists should be aware of these potential pitfalls and consider a broad differential diagnosis for each specific type of lesion involving the GU organs. The following summary of the contents presented at the 6th Annual Chinese American Pathologists Association (CAPA) Diagnostic Course (October 10-11, 2020), supplemented with relevant literature review, exemplifies the common diagnostic challenges and pitfalls for mass lesions of the GU system of adults, including adrenal gland, with emphasis on immunohistochemical and molecular updates when relevant.

OBJECTIVE.—

To describe the common mass lesions in the GU system of adults, including adrenal gland, with emphasis on the diagnostic challenges and pitfalls that may arise in the pathologic assessment, and to highlight immunohistochemical workups and emerging molecular findings when relevant.

DATA SOURCES.—

The contents presented at the course and literature search comprise our data sources.

CONCLUSIONS.—

The diagnostic challenges and pitfalls that arise in the pathologic assessment of the mass lesions in the GU system of adults, including adrenal gland, are common. We summarize the contents presented at the course, supplemented with relevant literature review, and hope to provide a diagnostic framework to evaluate these lesions in routine clinical practice.

Fumarate hydratase-deficient renal cell carcinoma: A tumor with diverse morphology including cannibalism, lymphocytic emperipolesis, and defective autophagy

We report the clinicopathological findings of the first series of 3 patients from Brazil with fumarate hydratase-deficient renal cell carcinoma. The clinicopathological findings disclosed a very aggressive tumor. All 3 patients had solitary tumor at the left side, metastasis and advanced stage at the time of diagnosis; were females with a median age of 40 years; had a history of uterine leiomyomas; and, at follow-up two patients are deceased and one patient alive. The microscopic findings of these 3 patients are in accordance with the literature disclosing a variety of morphologic features being papillary arrangement, eosinophilic cytoplasm, and prominent nucleoli surrounded by clear halo the constant and most frequent findings. Previously not reported in this tumor, we describe presence of cannibalism, lymphocytic emperipolesis, and cytoplasmic vacuoles with eosinophilic inclusions associated with overexpression of p62 in immunohistochemistry which is considered to be evidence of defective autophagy. Lymphocytic emperipolesis was a more frequent finding than cannibalism and immunohistochemistry for p62 was overexpressed only in the 2 patients disclosing cytoplasmic vacuoles with eosinophilic inclusions. The presence, frequency and significance of these novel findings should be checked in large series of this rare and aggressive tumor aiming to associate with clinical behavior and eventually influence the strategy of treatment.

[Oncocytic tumours of the kidney-new differential diagnoses]

BACKGROUND

Recent developments in differential diagnosis have led to new knowledge about oncocytic renal neoplasms.

OBJECTIVES

Overview of differential diagnosis of oncocytic tumours.

MATERIALS AND METHODS

We performed a literature search on oncocytic renal tumours and mapped known tumour types. Possible differential diagnoses are discussed.

RESULTS

Besides the tumour types already acknowledged by the 2016 WHO classification, there is new evidence regarding the group of hard-to-classify oncocytic neoplasms. Findings point to immunohistochemical and molecular characteristics that may lead to the establishment of new entities in the future. In addition, important differential diagnosis can now be identified, facilitating specific therapies for oncocytic renal tumours.

CONCLUSION

A correct diagnosis of oncocytic renal tumours not only improves prognostic assessment (and, if necessary, specific therapies) but is also clinically relevant regarding a possible association with hereditary tumour syndromes.

[FH-deficient renal cell carcinoma expands the spectrum of renal papillary tumors]

Fumarate hydratase (FH)-deficient renal cell carcinoma (RCC) is a distinct entity, which shows a biallelic inactivation of the FH gene that consequently leads to FH protein expression and function loss, respectively. This alteration leads to an accumulation of the oncometabolite fumarate in the citrate cycle and various disorders of the cell balance and DNA processing. FH-deficient RCC often shows a morphologically overlapping spectrum with papillary renal cell carcinoma (type 2), whereby a typical mixture of growth patterns including tubulo-cystic, cribriform, and/or solid differentiation can be observed. A characteristic but non-specific morphological feature is prominent eosinophilic, virus-inclusion body-like nucleoli with perinucleolar halos. Tumoral immunohistochemical loss of FH expression supports the diagnosis but may be preserved in rare cases. Most FH-deficient RCCs show very aggressive biological behavior and are often metastasized at the time of diagnosis. The initial description encompassed RCC in association with the hereditary leiomyomatosis and renal cell carcinoma (HLRCC) syndrome, which also includes cutaneous and uterine leiomyomas. However, current data also show an increasing proportion of sporadic cases, so that a distinction (hereditary vs. sporadic) seems appropriate. So far, few but promising data on effective systemic therapeutic options have been reported. In summary, precise diagnosis is of great importance due to the frequent aggressive biological behavior, potential need to deviate from the therapeutic standard, and the possible indicator of a hereditary disease.

[Clinicopathological features and prognosis of fumarate hydratase deficient renal cell carcinoma]

OBJECTIVE

To investigate the clinicopathological features and prognosis of fumarate hydratase deficient renal cell carcinoma (FH-RCC).

METHODS

Immunohistochemical (IHC) staining was used to detect the expression of fumarate hydratase (FH) in tumor tissues of 109 different types of renal cell carcinoma (RCC) patients aged 60 years and younger from the Department of Urology of Peking University First Hospital from January 2013 to December 2019. The clinicopathological data and prognosis of FH-RCC were collected and analyzed.

RESULTS

There were eleven patients with FH-negative expression. Seven were males and four females. The age of onset ranged 16-53 years (mean age: 36.7 years), and four female patients all had a history of uterine leiomyoma. Only one first-degree relative of one patient had renal cancer, and none of the patients had a history or family history of cutaneous leiomyomas. The diameter of the tumor was 2.1-12.0 cm (mean: 8.83 cm). Renal sinus or perirenal fat invasion was seen in nine cases, tumor thrombus in renal vein or inferior vena cava in six cases, lymph node metastasis in seven cases, adrenal gland invasion in four cases and splenic capsule invasion in one case. The cases were initially diagnosed as type Ⅱ papillary RCC (7/49, 14.3%), collecting duct carcinoma (2/9, 22.2%) and unclassified RCC (2/51, 3.9%). Tumor histopathology mostly showed a mixture of different structures, such as papillary, tubular cystic, solid, and so on. The most common histological structures were papillary (9/11, 81.8%) and tubular (8/11, 72.7%). Three cases had sarcomatoid areas. At least focal eosinophilic nucleolus (WHO/grades Ⅲ-Ⅳ) and perinuclear halo could be seen in all cases. Immunohistochemical (IHC) stains of most tumors were negative for CA9, CD10 and CK7. The results of fluorescence in situ hybridization (FISH) showed that there was no translocation or amplification of TFE3 gene in two cases with TFE3 IHC expression. All the patients were followed up for 11-82 months. Mean survival was 24 months. Five cases died of distant metastasis 9-31 months after operation (mean: 19 months), and five of the six patients alive had became metastatic.

CONCLUSION

Morphologically, FH-RCC overlaps with many types cell RCC. A mixture of papillary and tubular cystic arrangement is the most common growth pattern of FH-RCC. At least focally large and obvious eosinophilic nucleoli are an important histological feature of this tumor. The negative expression of FH can help to confirm the diagnosis. Young female RCC patients with uterine leiomyomas should be suspected of FH-RCC. Some FH-RCC cases lack clinical evidence. The suspicion raised by pathologists based on histological characteristics is often the key step to further genetic testing and the final diagnosis of the tumor.

Pathology and systemic therapy of non-clear cell renal cell carcinoma: an overview

Introduction: Non-clear cell renal cell carcinoma (nccRCC) represents a highly heterogenous group of kidney cancer entities. As most clinical trials predominantly include patients with clear cell RCC (ccRCC), nccRCC treatment guidelines are mainly extrapolated from recommendations in ccRCC. Here, we review and elucidate current data on the pathologic classification and treatment of nccRCC.Areas covered: This article gives an overview of the WHO classification of RCC, showing the histological diversity of nccRCC and focusing particularly on entities first characterized since 2016, their specific molecular behavior and their role as indicators for hereditary cancer syndromes. In this context, we discuss the available data on nccRCC treatment oprtions such as tyrosine kinase inhibitors, mammalian target of rapamycin inhibitors, cytotoxic chemotherapy, and immune checkpoint inhibitors.Expert opinion: Although nccRCCs are relatively uncommon, entities of this type account for a subgroup of up to 20-25% of all RCCs. Advances in histopathology and molecular genetics, together with evidence gained from retrospective and prospective clinical data, have improved understanding of these tumors in recent years. Nevertheless, selective trials of current and novel therapies including new targeted agents in patients with nccRCC are urgently needed to further improve treatment guidelines.

Immunoexpression of SDHB, FH, and CK20 among eosinophilic renal tumors: A tissue microarray study

BACKGROUND

Differential diagnosis can be a challenge for eosinophilic subtypes of renal cell tumors due to their overlapping histomorphological and immunohistochemical features. We aimed to investigate the frequency of rare variants of renal cell carcinomas (RCCs) such as succinate dehydrogenase-deficient RCC (SDDRCC), hereditary leiomyomatosis and RCC (HLRCC)-associated RCC, and eosinophilic, solid, and cystic RCC (ESCRCC) in our population.

MATERIALS AND METHODS

Renal tumors which could be considered in the eosinophilic tumor category were included: 91 conventional clear cell RCCs with eosinophilic cytoplasm, 72 papillary RCCs, 74 chromophobe RCCs, 88 oncocytomas, and 37 other rare subtypes. Using the tissue microarray method, succinate dehydrogenase B (SDHB), fumarate hydratase (FH), and cytokeratin 20 (CK20) antibodies were performed by immunohistochemistry. Immunohistochemistry was repeated on whole block sections for selected cases. The utility of these antibodies in the differential diagnosis was also investigated.

RESULTS

Loss of SDHB expression was detected in three tumors, two of which showed typical morphology for SDDRCC. In additional two tumors, SDHB showed weak cytoplasmic expression without a mitochondrial pattern (possible-SDHB deficient). None of the tumors showed loss of FH expression. Heterogeneous reactions were observed with SDHB and FH antibodies. Only one ESCRCC was detected with diffuse CK20 positivity.

CONCLUSION

SDDRCCs, HLRCC-associated RCCs, and ESCRCCs are very rare tumors depending on the population. Possible weak staining and focal loss of SDHB and FH expression should be kept in mind and genetic testing must be included for equivocal results.

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.

Low-Grade Fumarate Hydratase-Deficient Renal Cell Carcinoma in a 30-Year-Old Female

Fumarate hydratase (FH)-deficient renal cell carcinoma (RCC) is a rare and clinically aggressive RCC subtype that is commonly associated with the hereditary leiomyomatosis and renal cell carcinoma syndrome. The diagnostic hallmark of FH-deficient RCC is a high-grade microscopic appearance with prominent inclusion-like eosinophilic nucleoli and perinucleolar halos. Herein we report a case of an FH-deficient RCC in a 30-year-old female that exhibited low-grade nuclei and abundant eosinophilic cytoplasm, reminiscent of the clinically more indolent succinate dehydrogenase-deficient RCC subtype and the newly described eintity, eosinophilic, solid and cystic RCC. This case illustrates that FH-deficient RCC can have a wide spectrum of microscopic appearances, including low-grade eosinophilic RCC. In addition, it highlights that a low threshold to perform the immunohistochemical stains for FH and S-(2-succino) cysteine is warranted in RCC cases with unusual and even low-grade eosinophilic morphology.

Non-clear cell renal carcinomas: Review of new molecular insights and recent clinical data

Non-clear cell renal cell carcinomas (nccRCC) represent a highly heterogeneous group of kidney tumors, consisting of the following subtypes: papillary carcinomas, chromophobe renal cell carcinoma, so-called unclassified carcinomas or aggressive uncommon carcinomas such as Bellini carcinoma, renal cell carcinoma (RCC) with ALK rearrangement or fumarate hydratase-deficient RCC. Although non-clear cell cancers account for only 15 to 30% of renal tumors, they are often misclassified and accurate diagnosis continues to be an issue in clinical practice. Current therapeutic strategy of metastatic nccRCC is based primarily on guidelines established for clear cell tumors, the most common subtype, however this approach remains poorly defined. To date, published clinical trials for all histological nccRCC subtypes have been collectively characterized into one group, in contrast to clear cell RCC, and given the small numbers of cases, the interpretation of study results continues to be challenging. This review summarizes the available literature for each nccRCC subtype and highlights the lack of supportive evidence from prospective clinical trials and retrospective studies. Future trials should evaluate treatment approaches which focus on a specific histological subtype and progress in treating nccRCC will be contingent on understanding the unique biology of their individual histologies.

[Histological subtypes of renal cell carcinoma : Overview and new developments]

BACKGROUND

The classification of renal cell carcinoma (RCC) has changed remarkably in recent years.

OBJECTIVES

This is a short overview of the classification of RCC, focusing on new developments.

MATERIALS AND METHODS

A literature search was performed resulting in an overview of the classification of RCC. Emerging entities were discussed in detail.

RESULTS

Apart from the RCC subtypes in the WHO classification of 2016, several emerging entities came up over the last few years that are characterized by typical morphology, immunophenotype, and especially specific genetic alterations.

CONCLUSION

Precise classification of RCC is the key to better prognostic assessment with potential tumor-specific therapy and plays an important role in the recognition of possible association with hereditary tumor syndromes.

Renal cell carcinoma in young FH mutation carriers: case series and review of the literature

Hereditary Leiomyomatosis and Renal Cell Cancer (HLRCC) is an autosomal dominant syndrome caused by heterozygous pathogenic germline variants in the fumarate hydratase (FH) gene. It is characterized by cutaneous and uterine leiomyomas and an increased risk of developing renal cell carcinoma (RCC), which is usually adult-onset. HLRCC-related RCC tends to be aggressive and can metastasize even when the primary tumor is small. Data on children and adolescents are scarce. Herein, we report two patients from unrelated Dutch families, with HLRCC-related RCC at the ages of 15 and 18 years, and a third patient with an FH mutation and complex renal cysts at the age of 13. Both RCC’s were localized and successfully resected, and careful MRI surveillance was initiated to monitor the renal cysts. One of the patients with RCC subsequently developed an ovarian Leydig cell tumor. A review of the literature identified 10 previously reported cases of HLRCC-related RCC in patients aged younger than 20 years, five of them presenting with metastatic disease. These data emphasize the importance of recognizing HLRCC in young patients to enable early detection of RCC, albeit rare. They support the recommendations from the 2014 consensus guideline, in which genetic testing for FH mutations, and renal MRI surveillance, is advised for HLRCC family members from the age of 8–10 years onwards.

The Differential Diagnosis of Medullary-Based Renal Masses

CONTEXT.—

Renal malignancies can be divided into cortical- and medullary-based tumors, the latter of which classically infiltrate the renal parenchyma by extending between nonneoplastic structures. Although high-grade cortical tumors can rarely exhibit the same growth pattern, the infiltrative morphology should elicit a differential diagnosis to be considered in each case. However, these diagnoses can be challenging to distinguish, especially on small renal biopsy samples.

OBJECTIVE.—

To provide an overview of the clinical, gross, and microscopic findings; genetic and molecular alterations; and immunohistochemical evaluation of medullary-based renal tumors and other tumor types with overlapping morphologies and growth patterns.

DATA SOURCES.—

Literature review and personal observations were used to compile the information in this review.

CONCLUSIONS.—

Collecting duct carcinoma is a prototypical medullary-based tumor, and although diagnostic criteria exist, it remains a diagnosis of exclusion, especially with ancillary techniques aiding the recognition of established as well as more recently described neoplasms. Other medullary-based malignancies included in the differential diagnosis include renal medullary carcinoma/renal cell carcinoma unclassified with medullary phenotype, fumarate hydratase-deficient renal cell carcinoma, and upper tract urothelial carcinoma. Moreover, other rare entities should be excluded, including metastatic carcinoma, lymphoma, and melanoma. In addition to potential prognostic differences, accurate diagnoses can have important surgical and clinical management implications.

Management of 3 Cases of Pheochromocytoma During the COVID-19 Pandemic in New York City: Lessons Learned

The COVID-19 crisis placed a pause on surgical management of nonemergency cases of pheochromocytoma, and it was essential for endocrinologists to provide both resourceful and safe care. At the Mount Sinai Hospital in New York City during the peak of the pandemic, we encountered 3 patients with pheochromocytoma and mild symptoms that were medically managed for a prolonged period of time (7-18 weeks) prior to adrenalectomy. Patients were monitored biweekly via telemedicine, and antihypertensive medications were adjusted according to signs, symptoms, and adrenergic profiles. These cases demonstrate that prolonged medical management prior to surgery is feasible and effective in pheochromocytoma patients with mild symptoms and well-controlled blood pressures.

ALK rearranged renal cell carcinoma (ALK-RCC): a multi-institutional study of twelve cases with identification of novel partner genes CLIP1, KIF5B and KIAA1217

ALK rearranged renal cell carcinoma (ALK-RCC) has recently been included in 2016 WHO classification as a provisional entity. In this study, we describe 12 ALK-RCCs from 8 institutions, with detailed clinical, pathological, immunohistochemical (IHC), fluorescence in situ hybridization (FISH), and next generation sequencing (NGS) analyses. Patients' age ranged from 25 to 68 years (mean, 46.3 years). Seven patients were females and five were males (M:F = 1:1.4). Tumor size ranged from 17 to 70 mm (mean 31.5, median 25 mm). The pTNM stage included: pT1a (n = 7), pT1b (n = 1), and pT3a (n = 4). Follow-up was available for 9/12 patients (range: 2 to 153 months; mean 37.6 months); 8 patients were alive without disease and one was alive with distant metastases. The tumors demonstrated heterogeneous, 'difficult to classify' morphology in 10/12 cases, typically showing diverse architectural and cellular morphologies, including papillary, tubular, tubulocystic, solid, sarcomatoid (spindle cell), rhabdoid, signet-ring cell, and intracytoplasmic vacuoles, often set in a mucinous background. Of the remaining two tumors, one showed morphology resembling mucinous tubular and spindle cell renal cell carcinoma (MTSC RCC-like) and one was indistinguishable from metanephric adenoma. One additional case also showed a focal metanephric adenoma-like area, in an otherwise heterogeneous tumor. By IHC, all tumors were diffusely positive for ALK and PAX8. In both cases with metanephric adenoma-like features, WT1 and ALK were coexpressed. ALK rearrangement was identified in 9/11 tumors by FISH. ALK fusion partners were identified by NGS in all 12 cases, including the previously reported: STRN (n = 3), TPM3 (n = 3), EML4 (n = 2), and PLEKHA7 (n = 1), and also three novel fusion partners: CLIP1 (n = 1), KIF5B (n = 1), and KIAA1217 (n = 1). ALK-RCC represents a genetically distinct entity showing a heterogeneous histomorphology, expanded herein to include unreported metanephric adenoma-like and MTSC RCC-like variants. We advocate a routine ALK IHC screening for "unclassifiable RCCs" with heterogeneous features.

Genetic predisposition to neural crest-derived tumors: revisiting the role of KIF1B

OBJECTIVE

We previously described a family in which predisposition to pheochromocytoma (PCC) segregates with a germline heterozygous KIF1B nucleotide variant (c.4442G>A, p.Ser1481Asn) in three generations. During the clinical follow-up, one proband's brother, negative for the KIF1B nucleotide variant, developed a bilateral PCC at 31 years. This prompted us to reconsider the genetic analysis.

DESIGN AND METHODS

Germline DNA was analyzed by next-generation sequencing (NGS) using a multi-gene panel plus MLPA or by whole exome sequencing (WES). Tumor-derived DNA was analyzed by SnapShot, Sanger sequencing or NGS to identify loss-of-heterozygosity (LOH) or additional somatic mutations.

RESULTS

A germline heterozygous variant of unknown significance in MAX (c.145T>C, p.Ser49Pro) was identified in the proband's brother. Loss of the wild-type MAX allele occurred in his PCCs thus demonstrating that this variant was responsible for the bilateral PCC in this patient. The proband and her affected grandfather also carried the MAX variant but no second hit could be found at the somatic level. No other pathogenic mutations were detected in 36 genes predisposing to familial PCC/PGL or familial cancers by WES of the proband germline. Germline variants detected in other genes, TFAP2E and TMEM214, may contribute to the multiple tumors of the proband.

CONCLUSION

In this family, the heritability of PCC is linked to the MAX germline variant and not to the KIF1B germline variant which, however, may have contributed to the occurrence of neuroblastoma (NB) in the proband.

Renal Cell Tumors: Molecular Findings Reshaping Clinico-pathological Practice

Over the past 20 years, the number of subtypes of renal epithelial cell neoplasia has grown. This growth has resulted from detailed histological and immunohistochemical characterization of these tumors and their correlation with clinical outcomes. Distinctive molecular phenotypes have validated the unique nature of many of these tumors. This growth of unique renal neoplasms has continued after the 2016 World Health Organization (WHO) Classification of Tumours. A consequence is that both the pathologists who diagnose the tumors and the clinicians who care for these patients are confronted with a bewildering array of renal cell carcinoma variants. Many of these variants have important clinical features, i.e. familial or syndromic associations, genomics alterations that can be targeted with systemic therapy, and benignancy of tumors previously classified as carcinomas. Our goal in the review is to provide a practical guide to help recognize these variants, based on small and distinct sets of histological features and limited numbers of immunohistochemical stains, supplemented, as necessary, with molecular features.