Renal cell carcinoma with angioleiomyoma-like stroma and clear cell papillary renal cell carcinoma: exploring SDHB protein immunohistochemistry and the relationship to tuberous sclerosis complex

Morphological diversity in SDH-deficient renal carcinomas: a three-case exploration of variant features and dedifferentiation

Succinate dehydrogenase (SDH)-deficient renal cell carcinoma (RCC) is a rare subtype of renal neoplasm predominantly affecting younger individuals. It is characterized by germline mutations in SDHx genes, particularly type B. Histologically, SDH-deficient RCC features eosinophilic cytoplasmic cells forming solid nests or microcysts, sometimes entrapping normal tubules. We present three SDH-deficient RCC cases with overlapping morphological features with fumarate hydratase-deficient RCC and TFEB-rearranged RCC, an appearance that has not been previously described. All tumors lacked SDHB expression and harbored pathogenic SDHB mutations, with the germline nature confirmed in two cases. Metastasis developed in two patients. Our case set highlights the diagnostic challenges of molecularly defined renal tumors and expands the morphological spectrum of SDH-deficient RCC with unusual histological features. Clinically, these tumors appear to be aggressive.

Pathology of hereditary renal cell carcinoma syndromes: Tuberous sclerosis complex (TSC)

Tuberous sclerosis complex (TSC) is an autosomal dominant genetic disease characterized by hamartomatous tumors involving multiple organs such as the brain, skin, heart, lung and kidney. TSC is caused by inactivating mutations in TSC1/TSC2, which encodes hamartin and tuberin, respectively, and forms a complex that regulates mechanistic target of rapamycin complex 1 (mTORC1), resulting in cell overgrowth and oncogenesis. Since a leading cause of morbidity and mortality in TSC relates to chronic kidney disease and the ability to preserve renal function, this review describes the important pathologic findings in TSC-associated renal neoplasms and their correlating sporadic counterparts. The most common renal tumor in TSC patients are AMLs, followed by a heterogeneous spectrum of renal epithelial tumors, which may provide clues to establishing a diagnosis of TSC.

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.

Recent Advances in Renal Tumors with TSC/mTOR Pathway Abnormalities in Patients with Tuberous Sclerosis Complex and in the Sporadic Setting

A spectrum of renal tumors associated with frequent TSC/mTOR (tuberous sclerosis complex/mechanistic target of rapamycin) pathway gene alterations (in both the germline and sporadic settings) have recently been described. These include renal cell carcinoma with fibromyomatous stroma (RCC FMS), eosinophilic solid and cystic renal cell carcinoma (ESC RCC), eosinophilic vacuolated tumor (EVT), and low-grade oncocytic tumor (LOT). Most of these entities have characteristic morphologic and immunohistochemical features that enable their recognition without the need for molecular studies. In this report, we summarize recent advances and discuss their evolving complexity.

Kidney Tumors: New and Emerging Kidney Tumor Entities

This review summarizes current knowledge on several novel and emerging renal entities, including eosinophilic solid and cystic renal cell carcinoma (RCC), RCC with fibromyomatous stroma, anaplastic lymphoma kinase-rearranged RCC, low-grade oncocytic renal tumor, eosinophilic vacuolated tumor, thyroidlike follicular RCC, and biphasic hyalinizing psammomatous RCC. Their clinical features, gross and microscopic morphology, immunohistochemistry, and molecular and genetic features are described. The diagnosis of most of them rests on recognizing their morphologic features using immunohistochemistry. Accurate diagnosis of these entitles will further reduce the category of "unclassifiable renal carcinomas/tumors" and will lead to better clinical management and improved patient prognostication.

Reprint of: lessons from histopathologic examination of nephrectomy specimens in patients with tuberous sclerosis complex: cysts, angiomyolipomas & renal cell carcinoma

Renal manifestations in patients with tuberous sclerosis complex (TSC) include cysts, angiomyolipoma, and renal cell carcinoma. Unlike many hereditary predisposition syndromes, the spectrum of renal tumors in TSC patients (including both angiomyolipoma and renal cell carcinoma) is broad, with significant morphologic heterogeneity. An improved understanding of histopathologic findings in TSC patients and associated clinicopathologic correlates has significant implications not just in establishing a diagnosis of TSC, but also in the recognition of sporadic tumors occurring secondary to somatic alterations of TSC1/TSC2/MTOR pathway genes and accurate prognostication. In this review, we have discussed issues relevant to clinical management based on histopathologic findings in nephrectomy specimens from patients with TSC. This includes discussions related to screening for TSC, diagnosis of PKD1/TSC2 contiguous gene deletion syndrome, the morphologic spectrum of angiomyolipoma and renal epithelium-derived neoplasia, including the risk of disease progression.

TSC/MTOR mutated renal cell carcinoma with leiomyomatous stroma is a distinct entity: a comprehensive study of 12 cases

The 2016 World Health Organization (WHO) Classification of Tumors of the Urinary System includes renal cell carcinoma (RCC) with leiomyomatous stroma (RCC-LS) as a provisional category. Recent studies have shown that this category includes at least 4 subtypes: clear cell (CCRCC), clear cell papillary renal cell tumor (CCPRCT), ELOC (TCEB1) mutated, and a subtype of RCC with TSC/MTOR mutations. The most recent 2022 World Health Organization (WHO) Classification of Tumors of the Urinary System includes ELOC mutated RCC-LS as a distinct entity but does not address any other renal tumors with smooth muscle stroma. We reviewed >500 cases of RCC with clear cell phenotype and identified 12 cases that exhibited prominent smooth muscle stroma, of which 4 of the cases had been previously reported. Review of the H&E revealed that all of the tumors were circumscribed with nested, solid, tubular, and tubulopapillary architecture. The epithelium was intimately embedded in the rich smooth muscle stroma. WHO/ISUP grade corresponded to grade 3 and 4. Nuclei were randomly distributed and the cytoplasm had predominantly clear and occasionally flocculent appearance. Immunohistochemically, all the cases showed membranous CAIX staining, although the pattern was combined cup and box-shaped. CK7 was positive in all cases ranging from 25% to 100% of cells. Membranous and apical staining of CD10 was present in all cases. Next generation sequencing (NGS) of these cases identified mutations in TSC1 (n = 4), TSC2 (n = 3), and MTOR (n = 4) with one case exhibiting loss of TSC1. This descriptive study, although small, demonstrates the difficulty in applying the current WHO provisional criteria at a single institution. Given the heterogeneity seen with these cases, we suggest following up an immunohistochemical panel of CAIX, CK7, and CD10 with molecular diagnostic studies to assist in the diagnosis of TSC/MTOR associated RCC-LS, which we believe is a distinct entity.

Kidney Tumors: New and Emerging Kidney Tumor Entities

This review summarizes current knowledge on several novel and emerging renal entities, including eosinophilic solid and cystic renal cell carcinoma (RCC), RCC with fibromyomatous stroma, anaplastic lymphoma kinase-rearranged RCC, low-grade oncocytic renal tumor, eosinophilic vacuolated tumor, thyroidlike follicular RCC, and biphasic hyalinizing psammomatous RCC. Their clinical features, gross and microscopic morphology, immunohistochemistry, and molecular and genetic features are described. The diagnosis of most of them rests on recognizing their morphologic features using immunohistochemistry. Accurate diagnosis of these entitles will further reduce the category of "unclassifiable renal carcinomas/tumors" and will lead to better clinical management and improved patient prognostication.

How New Developments Impact Diagnosis in Existing Renal Neoplasms

In recent years, several emerging diagnostic entities have been described in renal cell carcinoma (RCC). However, our understanding of well-known and established entities has also grown. Clear cell papillary RCC is now relabeled as a tumor rather than carcinoma in view of its nonaggressive behavior. Renal tumors with a predominantly infiltrative pattern are very important for recognition, as most of these have aggressive behavior, including fumarate hydratase-deficient RCC, SMARCB1-deficient medullary carcinoma, collecting duct carcinoma, urothelial carcinoma, and metastases from other cancers.

Lessons from histopathologic examination of nephrectomy specimens in patients with tuberous sclerosis complex: cysts, angiomyolipomas, and renal cell carcinoma

Renal manifestations in patients with tuberous sclerosis complex (TSC) include cysts, angiomyolipoma, and renal cell carcinoma. Unlike many hereditary predisposition syndromes, the spectrum of renal tumors in TSC patients (including both angiomyolipoma and renal cell carcinoma) is broad, with significant morphologic heterogeneity. An improved understanding of histopathologic findings in TSC patients and associated clinicopathologic correlates has significant implications not just in establishing a diagnosis of TSC, but also in the recognition of sporadic tumors occurring secondary to somatic alterations of TSC1/TSC2/MTOR pathway genes and accurate prognostication. In this review, we have discussed issues relevant to clinical management based on histopathologic findings in nephrectomy specimens from patients with TSC. This includes discussions related to screening for TSC, diagnosis of PKD1/TSC2 contiguous gene deletion syndrome, the morphologic spectrum of angiomyolipoma and renal epithelium-derived neoplasia, including the risk of disease progression.

Renal Cell Carcinoma in Tuberous Sclerosis Complex

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder in which renal manifestations are prominent. There are three major renal lesions in TSC: angiomyolipomas, cysts, and renal cell carcinoma (RCC). Major recent advances have revolutionized our understanding of TSC-associated RCC, including two series that together include more than 100 TSC-RCC cases, demonstrating a mean age at onset of about 36 years, tumors in children as young as 7, and a striking 2:1 female predominance. These series also provide the first detailed understanding of the pathologic features of these distinctive tumors, which include chromophobe-like features and eosinophilia, with some of the tumors unclassified. This pathologic heterogeneity is distinctive and reminiscent of the pathologic heterogeneity in Birt-Hogg-Dube-associated RCC, which also includes chromophobe-like tumors. Additional advances include the identification of sporadic counterpart tumors that carry somatic TSC1/TSC2/mTOR mutations. These include unclassified eosinophilic tumors, eosinophilic solid cystic RCC (ESC-RCC), and RCC with leiomyomatous stroma (RCCLMS). A variety of epithelial renal neoplasms have been identified both in patients with tuberous sclerosis complex (TSC) and in the nonsyndromic setting associated with somatic mutations in the TSC1 and TSC2 genes. Interestingly, whether tumors are related to a germline or somatic TSC1/2 mutation, these tumors often display similar morphologic and immunophenotypic features. Finally, recent work has identified molecular links between TSC and BHD-associated tumors, involving the TFEB/TFE3 transcription factors.

Renal cell carcinoma with leiomyomatous stroma in tuberous sclerosis complex: a distinct entity

Renal cell carcinoma with leiomyomatous stroma (RCCLS) is an emerging entity frequently associated with tuberous sclerosis complex (TSC). We described herein a series of RCCLS in TSC patients at pathological and cytogenetic levels. Three male patients with TSC and RCCLS were identified between 2000 and 2019 at the University Hospital of Rennes. Histologically, the architecture was tubulo-papillary with thick bundles of smooth muscle cells. The tumor cells showed clear cytoplasm with eosinophilic globules. The immunohistochemical profile was identical with an intense positivity of CK7, CAIX, and CD10 and a heterogeneous positivity of CK20. SDHB was low but positive and TFE3 was not expressed. Comparative genomic hybridization (CGH) did not show any quantitative chromosome abnormality. No recurrence was observed with a median follow-up of 4 years. RCCLS in TSC patients has morphological, immunohistochemical, and cytogenetic distinct features that could constitute a distinct entity and a sentinel manifestation for the diagnosis of TSC.

"Renal Cell Carcinoma With Leiomyomatous Stroma" Harbor Somatic Mutations of TSC1, TSC2, MTOR, and/or ELOC (TCEB1): Clinicopathologic and Molecular Characterization of 18 Sporadic Tumors Supports a Distinct Entity

Renal cell carcinoma with (angio) leiomyomatous stroma (RCCLMS) is included as a provisional entity in the 2016 World Health Organization (WHO) classification of renal epithelial neoplasia; however, debate remains whether it represents a distinct entity or a heterogenous group of renal cell carcinomas (RCCs) with overlapping morphology. Also, its relationship to similar tumors occurring in the setting of tuberous sclerosis complex (TSC) is not fully addressed. We analyzed the clinicopathologic, immunohistochemical, and molecular characteristics of 23 sporadic RCCs associated with smooth muscle stroma and classified them into 2 groups, independent of molecular results: (1) RCCLMS (n=18) and (2) clear cell renal cell carcinoma (CCRCC) (n=5). The classification of a case as "RCCLMS" was based on morphologic comparison with 5 "index" RCCs from 3 patients with TSC showing similar features and the presence of diffuse CK7 expression. To investigate mutational and copy number alterations, a 170-gene solid tumor panel was utilized to sequence 14 RCCLMSs and control of 5 CCRCCs. Also, 4 RCCLMSs, suspicious for chromosome 8 monosomy, were further evaluated by a broader 479 gene sequencing panel that included ELOC (also referred to as TCEB1). Clinical information and follow-up data were obtained from electronic medical records. The mean age of patients with RCCLMS was 52 years (range, 33 to 69) with male:female ratio of 1:2. Macroscopically, all tumors were solitary and predominantly (82%) tan/red, circumscribed, and solid. The average tumor size was 2.3 cm (range, 1.1 to 4.5). Microscopically, the distinctive feature included tumor nodules of elongated and frequently branching tubules lined by cells with voluminous clear to mildly eosinophilic cytoplasm (100%), separated by focal to prominent smooth muscle stroma. Additional frequently identified features included: biphasic pattern of collapsed acini surrounding tubules with voluminous cytoplasm (50%), focal papillary architecture (39%), peritumoral lymphoid aggregates (39%), and hemosiderin-laden macrophages (33%). All 11 (100%) RCCLMSs with available staging information were pT1; 78% were WHO/International Society of Urologic Pathology (ISUP) grade 2 and 22% grade 3. Immunophenotypically, RCCLMSs were characterized by diffuse CK7, CAM5.2 and CD10 reactivity (100%). All patients with available follow-up (n=10) were alive and without disease progression after a mean and median follow-up of 25.2 (range: 1 to 58) and 25 months, respectively. The molecular results showed recurrent mutations in all RCCLMS: TSC1 (4), TSC2 (4), MTOR (6), and/or ELOC (2). Five control CCRCCs demonstrated primary alterations in VHL gene, while all 14 RCCLMS cases tested had intact VHL gene. Of 2 RCCLMSs with confirmed monosomy 8, 1 showed a hotspot ELOC mutation without TSC/MTOR mutations, and 1 showed a previously undescribed 3-bp in-frame ELOC deletion, along with a truncating TSC1 mutation. In conclusion, RCCLMS, as defined herein, harbors recurrent mutations of TSC1/TSC2, MTOR, and/or ELOC, consistent with hyperactive MTOR complex. Our findings argue that these tumors represent the sporadic counterpart to morphologically identical tumors occurring in TSC patients. Finally, the data support that RCCLMS is a novel subtype of RCC with unique morphologic, immunohistochemical, and molecular characteristics that is distinct from CCRCC and clear cell-papillary RCC.

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.

Molecular Genetics of Renal Cell Tumors: A Practical Diagnostic Approach

Renal epithelial cell tumors are composed of a heterogeneous group of tumors with variable morphologic, immunohistochemical, and molecular features. A "histo-molecular" approach is now an integral part of defining renal tumors, aiming to be clinically and therapeutically pertinent. Most renal epithelial tumors including the new and emerging entities have distinct molecular and genetic features which can be detected using various methods. Most renal epithelial tumors can be diagnosed easily based on pure histologic findings with or without immunohistochemical examination. Furthermore, molecular-genetic testing can be utilized to assist in arriving at an accurate diagnosis. In this review, we presented the most current knowledge concerning molecular-genetic aspects of renal epithelial neoplasms, which potentially can be used in daily diagnostic practice.

Immunohistochemical Pitfalls in Genitourinary Pathology: 2018 Update

Immunohistochemistry may be a very useful adjunct to morphologic diagnosis in many areas of surgical pathology, including genitourinary pathology. In this review, we address common diagnostic dilemmas where immunophenotypic analysis may be utilized and we highlight pitfalls specific to each scenario. For prostate, we review the diagnosis of limited prostatic adenocarcinoma and the distinction of high-grade prostatic adenocarcinoma from urothelial carcinoma. We also cover markers of urothelial lineage in the diagnosis of metastatic carcinoma of unknown primary site. In the kidney, distinction of poorly differentiated renal cell carcinoma from urothelial carcinoma and epithelioid angiomyolipoma, adjuncts to the recognition of hereditary renal neoplasia, and the diagnosis of metastatic renal cell carcinoma are discussed. Finally, for testis we address distinction of germ cell tumors from sex cord-stromal tumors, as well as the diagnosis of metastatic germ cell tumors.

Atypical tuberous sclerosis complex presenting as familial renal cell carcinoma with leiomyomatous stroma

We report an atypical tuberous sclerosis complex (TSC) phenotype presenting as familial multiple renal cell carcinomas (RCCs) with (angio)leiomyomatous stroma (RCCLS) (5/7 familial RCCs) on a background of multiple angiomyolipomas, hypopigmented skin macules, and absence of neurological anomalies. In the index case and three relatives, germline genetic testing identified a heterozygous TSC2 missense pathogenic variant [c.2714 G > A, (p.Arg905Gln)], a rare TSC‐associated alteration which has previously been associated with a milder TSC phenotype. Whole‐exome sequencing of five RCCs from the index case and one RCC from his mother demonstrated either unique tumour‐specific deleterious second hits in TSC2 or significant allelic imbalance at the TSC2 gene locus (5/6 RCCs). This study confirms the key tumourigenic role of tumour‐specific TSC2 second hits in TSC‐associated RCCs and supports the notion that RCCLS may be strongly related to abnormalities of the mTOR pathway.