Renal small cell oncocytoma with pseudorosettes

Renal Oncocytoma: The Diagnostic Challenge to Unmask the Double of Renal Cancer

Renal oncocytoma represents the most common type of benign neoplasm that is an increasing concern for urologists, oncologists, and nephrologists due to its difficult differential diagnosis and frequent overtreatment. It displays a variable neoplastic parenchymal and stromal architecture, and the defining cellular element is a large polygonal, granular, eosinophilic, mitochondria-rich cell known as an oncocyte. The real challenge in the oncocytoma treatment algorithm is related to the misdiagnosis due to its resemblance, at an initial radiological assessment, to malignant renal cancers with a completely different prognosis and medical treatment. Unfortunately, percutaneous renal biopsy is not frequently performed due to the possible side effects related to the procedure. Therefore, the majority of oncocytoma are diagnosed after the surgical operation via partial or radical nephrectomy. For this reason, new reliable strategies to solve this issue are needed. In our review, we will discuss the clinical implications of renal oncocytoma in daily clinical practice with a particular focus on the medical diagnosis and treatment and on the potential of novel promising molecular biomarkers such as circulating microRNAs to distinguish between a benign and a malignant lesion.

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.

Small-cell variant renal oncocytoma: Case report on its clinicopathological and genetic characteristics and literature review

INTRODUCTION

Small-cell variant of RO is a rare subtype of renal tumor that can be easily misdiagnosed. To date, only 20 cases had been reported, with its genetic alterations largely unknown due to insufficient information.

MATERIALS AND METHODS

We report a case of the tumor with genetic characterization using exome sequencing chip. We also reviewed literature on this lesion to summarize clinicopathological presentation and differential diagnosis of the tumor.

DISCUSSION

Grossly, the tumor is yellow to grayish brown, with clear boundary, central scar, or cystic degeneration. Microscopically, small-cell variant RO show scant eosinophilic cytoplasm with small-round nuclei, arranged in small acini and tubules. Nucleoli and necrosis are rarely observed. Immunohistochemically, the tumor is positive for EMA, cytokeratin 18, CD117 and E-cadherin. Genetically, 4745 differentially expressed genes in this tumor, which encode tricarboxylic acid cycle enzymes and are involved in mitochondrial respiratory chain. This result strongly supports the diagnosis of small cell variant of RO. Findings from the molecular genetic analysis of our case suggests that metabolic pathway-related genes (PIK3R5, PI3KCB, PLA2G4E, PLA2G2A, PLA2G6, PLCB4, PLCG2) may be exploited as potential targets for diagnosis and treatment when necessary. These genes may provide new clues for future research.

CONCLUSION

Small-cell variant of RO is considered benign renal neoplasms with good prognosis. A histochemical and immunohistochemical stains assist in diagnosis of this tumor. Definitive diagnosis can help avoid unnecessary total renal nephrectomy. The exact mechanism of Small-cell variant of RO remains to be further investigated.

Modern Pathologic Diagnosis of Renal Oncocytoma

Oncocytoma is a well-defined benign renal tumor, with classic gross and histologic features, including a tan or mahogany-colored mass with central scar, microscopic nested architecture, bland cytology, and round, regular nuclei with prominent central nucleoli. As a result of variations in this classic appearance, difficulty in standardizing diagnostic criteria, and entities that mimic oncocytoma, such as eosinophilic variant chromophobe renal cell carcinoma and succinate dehydrogenase-deficient renal cell carcinoma, pathologic diagnosis remains a challenge. This review addresses the current state of pathologic diagnosis of oncocytoma, with emphasis on modern diagnostic markers, areas of controversy, and emerging techniques for less invasive diagnosis, including renal mass biopsy and advanced imaging.

The clinicopathological, ultrastructural, genetic features and diagnosis of small cell variant renal oncocytoma

The small cell variant renal oncocytoma is until now a rarely described and easily misdiagnosed subtype of renal oncocytoma. The tissue morphology, immunohistochemical profile, ultrastructural and molecular characteristics of four cases of small cell variant renal oncocytoma were analyzed and the literature was reviewed. The patients were three women and one man with ages ranging from 51 to 76 years. The size of the tumors ranged from 3 to 8.5 cm in diameter. The follow-up duration ranged from 6 to 58 months. All patients lived uneventfully without tumor recurrence or metastasis. The tumors were grayish yellow to brown, well demarcated, with a central scar or cystic change. Microscopically, the tumor was arranged in lobular structure containing dense small acini or tubular structures, with small cells featuring weak eosinophilic and scant cytoplasm, small round nuclei and inconspicuous nucleoli. No mitotic figures or necrosis were discerned. The immunohistochemical profile of small cell variant of renal oncocytoma is partially consistent with classic oncocytoma, expressing EMA, CK18, CD117 and E-cad. However, MITO and S-100A1 were intensively expressed in classic RO, but neither of them was expressed in small cell variant RO. Ultrastructurally, a small number of organelles was revealed in the tumor cell, including a few mitochondria, lysosomes and microvilli, less than those in the classic oncocytoma. No genetic aberrations were found in all cases regardless of clinicopathological characteristics and tissue types. Small cell variant renal oncocytoma of the kidney is frequently difficult to be differentiated from other benign and malignant small cell tumors with eosinophilic cytoplasm. The immunohistochemical profile, ultrastructural and genetic features of the tumor are integrally presented here for the first time. Acquaintance with the special characteristics of the tumor could facilitate the correct diagnosis of the tumor.

Overexpression of the cell adhesion molecule claudin-9 is associated with invasion in pituitary oncocytomas

Pituitary oncocytoma is a subtype of nonfunctioning pituitary adenomas with the potential to be locally invasive. Currently, surgery is the most effective treatment, whereas functional pituitary adenomas can be treated by drugs. We analyzed the invasiveness of pituitary oncocytomas to identify biomarkers that may be useful for guiding future therapeutic decision making. To identify important biomarkers of pituitary oncocytomas, 20 oncocytomas that were negative for hormone-specific immunostaining were confirmed by anti-mitochondria antibody immunostaining and electron microscopy. Our clinical phenotype data showed a prominent male predilection (85%). These tumors were classified as invasive or noninvasive based on preoperative magnetic resonance imaging, intraoperative records, and pathology slide. We observed significantly different expression profiles between pituitary oncocytomas (n = 3) and normal pituitary glands (n = 3). A total of 1937 genes were differentially expressed between the pituitary oncocytomas and normal pituitary glands. Among these 1937 genes, 954 were up-regulated and 983 were down-regulated in pituitary oncocytomas. The most significantly altered gene, claudin-9 (CLDN9), was further confirmed by quantitative real-time polymerase chain reaction, Western blot, and immunohistochemical staining in 10 invasive pituitary oncocytoma samples and 10 noninvasive pituitary oncocytoma samples. High levels of CLDN9 were found in the pituitary oncocytomas, whereas low levels were detected in normal pituitary glands. In addition, the CLDN9 expression level was higher in invasive oncocytomas compared with noninvasive oncocytomas. Bioinformatics Gene Ontology analysis was performed to better understand the critical role of CLDN9 in the development and progression of oncocytomas. Consequently, CLDN9 may be an important biomarker for invasive pituitary oncocytomas.