Low-grade oncocytic tumour (LOT) of the kidney is characterised by GATA3 positivity, FOXI1 negativity and mTOR pathway mutations

GATA3 Expression in Solid Vimentin-Negative Eosinophilic Renal Epithelial Tumors-A Comprehensive Study of 48 Tumors

Vimentin-negative solid eosinophilic renal tumors, such as renal oncocytoma, chromophobe renal cell carcinoma (chromophobe RCC), low-grade oncocytic tumor (LOT) of the kidney, and eosinophilic vacuolated tumor (EVT), often present diagnostic challenge to pathologists as they can have significant morphologic overlap. Recent studies have shown that the LOT is consistently positive for GATA3. To test the utility of GATA3 in this potentially challenging diagnostic setting, we investigated GATA3 expression in 48 vimentin-negative solid eosinophilic renal tumors with unequivocal diagnosis, which included 19 LOTs, 3 EVTs, 12 chromophobe RCCs, 11 renal oncocytomas (ROs), and 3 FLCN-mutated renal tumors. GATA3 was at least focally positive in 89% of the LOTs (17/19), 67% of the EVTs (2/3), and 33% of the chromophobe RCCs (4/12) and was negative in all ROs (0/11) and FLCN-mutated renal tumors (0/3). Our study shows that GATA3 can be useful in differentiating between LOT and RO, but it can be focally positive in many tumors of EVT and chromophobe RCC. Therefore, GATA3 could be useful as a panel of immunohistochemical stains that are used in diagnostic algorithm of vimentin-negative solid eosinophilic renal tumors. However, one should not solely rely on GATA3 as vimentin-negative solid eosinophilic renal tumors can have overlapping GATA3 expression.

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.

Whole exome sequencing identified mutations of forkhead box I 1 (FOXI1), keratin 6 C (KRT6C) and gap junction protein delta 2 (GJD2) in a low-grade oncocytic tumor of the kidney: a case report

BACKGROUND

Low-grade oncocytic tumor (LOT) of the kidney is an emerging entity among renal oncocytic tumors. While the histological features of LOT of the kidney are similar to those of renal oncocytoma, LOT immunohistochemically expresses keratin 7 (KRT7) but not KIT while renal oncocytoma expresses KIT. Molecular analyses of LOTs of the kidney using next generation sequencing revealed those tumors harbor mutations of mTOR-related genes.

CASE PRESENTATION

An 80-year-old Japanese man with a history of clear cell renal cell carcinoma and prostatic cancer underwent resection of the tumor of the right kidney, 10 mm in diameter, which was monitored for six years. The tumor was histologically composed of oncocytic cells that expressed KRT7, vimentin, SDHA, SDHB and fumarate hydratase, but not KIT, GATA3 and alpha-methylacyl-CoA racemase. We diagnosed the tumor as LOT of the kidney. Whole-exome sequencing of the LOT revealed single nucleotide variants in the DNA-binding region of forkhead box I1 (FOXI1), the coil 1B domain of keratin 6 C (KRT6C) and the intracytoplasmic region of gap junction delta 2 (GJD2), which encodes connexin 36. However, there was no mutations in mTOR-related genes. No copy number alterations were detected in the tumor.

CONCLUSIONS

We report three mutations in genes that have not been previously reported in LOT of the kidney. The genes are not related to the mTOR pathway. Therefore, LOT of the kidney might occur through several mechanisms and/or include several types of renal oncocytic tumors.

Charting New Territory With a Novel WHO Provisional Category: A Case Study of a Low-Grade Oncocytic Tumor (LOT) in the Kidney

A low-grade oncocytic tumor of the kidney (LOT) is a distinctive entity categorized under the 2022 World Health Organization (WHO) classification as "Other oncocytic tumors of the kidney." It represents a unique subset of oncocytic tumors, distinct from oncocytoma and chromophobe renal cell carcinoma. Characterized by bland oncocytic cells that diffusely express CK7 and lack CD117 expression, LOT typically manifests as a solitary, small lesion with a low stage. Available data suggest that LOT follows an indolent clinical course. Herein, we present a case of LOT in a 64-year-old male with a favorable course at a one-year follow-up. Understanding the clinical, morphological, and immunophenotypic features of LOT is paramount for accurate identification and characterization. This knowledge facilitates more conservative surgical and clinical management, optimizing patient care and outcomes.

Mechanistic Target of Rapamycin Kinase is a Common Convergent Pathway to Renal Neoplasia: A Contemporary Review

Mechanistic target of rapamycin kinase (mTOR) is a member of the phosphatidylinositol-3-hydroxide kinase (PI3 K)-related protein kinase family that functions as a central regulator of cell growth, metabolism, proliferation, and survival. The role of the TSC-mTOR signaling pathway in kidney tumors has been implicated in some hamartoma syndromes; however, with the advent and wide utilization of molecular studies, a growing number of kidney tumors have been linked to somatic or germline mutations involving genes that encode for this pathway, including eosinophilic solid and cystic renal cell carcinoma, low-grade oncocytic tumor, eosinophilic vacuolated tumor, renal cell carcinoma with fibromyomatous stroma and angiomyolipoma, among others. Herein, we review the contemporary developments of mTOR pathway-related renal neoplasia, focusing on the clinicopathologic features of the tumor entities.

Frequency and clinicopathologic features of renal low-grade oncocytic tumour and eosinophilic vacuolated tumour: reclassification of 605 eosinophilic tumours including patients managed with active surveillance

AIMS

Low-grade oncocytic tumour (LOT) and eosinophilic vacuolated tumour (EVT) are recently described emerging entities, which demonstrate distinct features but are not yet recognised as separate neoplasms in the fifth WHO classification. Published series to date have been largely multi-institutional and based on surgically resected tumours. This study aims to determine the frequency, clinicopathologic features and outcome of LOT and EVT in a single institutional series of oncocytic/eosinophilic renal neoplasms, including patients managed with active surveillance and non-surgical intervention.

METHODS AND RESULTS

Cases were identified from a consecutive institutional series of in-house renal tumours diagnosed on biopsy and/or nephrectomy (2003-2023). Tumours with a diagnosis or differential diagnosis of oncocytoma, chromophobe renal cell carcinoma or oncocytic neoplasm not otherwise specified (including LOT, EVT and tumours with overlapping hybrid features) were retrospectively reviewed and classified/reclassified.In total, 605 oncocytic/eosinophilic renal neoplasms were reviewed, among which 33 LOT (5.5%) and 5 EVT (0.8%) were identified. LOT were CK7+, CD117- and GATA3+ (94%). EVT were CD117+, CK7 focal+ (80%) and cathepsin K+ (80%). At the median follow-up of 34 months (range 2-253) and 56 months (range 8-90) for LOT and EVT, respectively, there was no evidence of recurrence following ablation/surgical resection, metastasis or death from disease for all patients, including the 22 managed with active surveillance (20 LOT and 2 EVT).

CONCLUSIONS

LOT and EVT comprised a minority of oncocytic renal neoplasms in this series. We report a large institutional series including patients managed non-surgically, with no adverse outcome, adding to the existing literature indicating a benign outcome.

Low-grade oncocytic tumor: a review of radiologic and clinical features

PURPOSE

The 2022 World Health Organization classification of renal neoplasia expanded the spectrum of oncocytic neoplasms to encompass newly established and emerging entities; one of the latter is the low-grade oncocytic tumor (LOT). This study reports the radiologic appearance and clinical behavior of LOT.

METHODS

In this IRB-approved, HIPPA-compliant retrospective study, our institution's pathology database was searched for low-grade oncocytic tumors or neoplasms. Patient age, gender, and comorbidities were obtained from a review of electronic medical records, and imaging characteristics of the tumors were assessed through an imaging platform.

RESULTS

The pathology database search yielded 14 tumors in 14 patients. Four patients were excluded, as radiologic images were not available in three, and one did not fulfill diagnostic criteria after pathology re-review. The resulting cohort consisted of 10 tumors (median diameter 2.3 cm, range 0.7-5.1) in 10 patients (median age 68 years, range 53-91, six women). All tumors presented as a solitary, well-circumscribed, mass with solid components. All enhanced as much or almost as much as adjacent renal parenchyma; all but one enhanced heterogeneously. None had lymphadenopathy, venous invasion, or metastatic disease at presentation or at clinical follow-up (median, 22.2 months, range 3.4-71.6). Among five tumors undergoing active surveillance, mean increase in size was 0.4 cm/year at imaging follow-up (median 16.7 months, range 8.9-25.4).

CONCLUSION

LOT, a recently described pathologic entity in the kidney, can be considered in the differential diagnosis of an avidly and typically heterogeneously enhancing solid renal mass in an adult patient.

L1 Cell Adhesion Molecule (L1CAM) Expression and Molecular Alterations Distinguish Low-Grade Oncocytic Tumor From Eosinophilic Chromophobe Renal Cell Carcinoma

Renal low-grade oncocytic tumor (LOT) is a recently recognized renal cell neoplasm designated within the "other oncocytic tumors" category in the 2022 World Health Organization classification system. Although the clinicopathologic, immunohistochemical, and molecular features reported for LOT have been largely consistent, the data are relatively limited. The morphologic overlap between LOT and other low-grade oncocytic neoplasms, particularly eosinophilic chromophobe renal cell carcinoma (E-chRCC), remains a controversial area in renal tumor classification. To address this uncertainty, we characterized and compared large cohorts of LOT (n = 67) and E-chRCC (n = 69) and revealed notable differences between the 2 entities. Clinically, LOT predominantly affected women, whereas E-chRCC showed a male predilection. Histologically, although almost all LOTs were dominated by a small-nested pattern, E-chRCC mainly showed solid and tubular architectures. Molecular analysis revealed that 87% of LOT cases harbored mutations in the tuberous sclerosis complex (TSC)-mTOR complex 1 (mTORC1) pathway, most frequently in MTOR and RHEB genes; a subset of LOT cases had chromosomal 7 and 19q gains. In contrast, E-chRCC lacked mTORC1 mutations, and 60% of cases displayed chromosomal losses characteristic of chRCC. We also explored the cell of origin for LOT and identified L1 cell adhesion molecule (L1CAM), a collecting duct and connecting tubule principal cell marker, as a highly sensitive and specific ancillary test for differentiating LOT from E-chRCC. This distinctive L1CAM immunohistochemical labeling suggests the principal cells as the cell of origin for LOT, unlike the intercalated cell origin of E-chRCC and oncocytoma. The ultrastructural analysis of LOT showed normal-appearing mitochondria and intracytoplasmic lumina with microvilli, different from what has been described for chRCC. Our study further supports LOT as a unique entity with a benign clinical course. Based on the likely cell of origin and its clinicopathologic characteristics, we propose that changing the nomenclature of LOT to "Oncocytic Principal Cell Adenoma of the Kidney" may be a better way to define and describe this entity.

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.