Multifocal renal oncocytoma in a patient with Von Hippel-Lindau mutation

Potential Role of VHL, PTEN, and BAP1 Mutations in Renal Tumors

The genetic profiling of renal tumors has revealed genomic regions commonly affected by structural changes and a general genetic heterogeneity. The VHL, PTEN, and BAP1 genes are often mutated in renal tumors. The frequency and clinical relevance of these mutations in renal tumors are still being researched. In our study, we investigated VHL, PTEN, and BAP1 genes and the sequencing of 24 samples of patients with renal tumors, revealing that VHL was mutated at a noticeable frequency (25%). Six of the investigated samples showed mutations, and one genetic polymorphism (rs779805) was detected in both heterozygote and homozygote forms. PTEN gene mutation was observed in only one sample, and one specimen showed genetic polymorphism. In the case of the BAP1 gene, all of the samples were wild types. Interestingly, VHL mutation was detected in two female patients diagnosed with AML and in one with oncocytoma. We assume that VHL or PTEN mutations may contribute to the development of human renal cancer. However, the overall mutation rate was low in all specimens investigated, and the development and prognosis of the disease were not exclusively associated with these types of genetic alterations.

High-Resolution Ultrasonography of Renal Oncocytoma Presenting with Symptomatic Hematuria and Urinary Bladder Clot Retention-A Rare Occurrence

Renal oncocytomas are asymptomatic, benign tumors often encountered incidentally on various imaging modalities. Renal oncocytomas comprise 5–7% of primary renal neoplasms and are derived from cells of the distal renal tubule. We present a case report of renal oncocytoma in a 22-year-old male having right-sided flank pain and symptomatic gross hematuria with a giant urinary bladder clot retention. The tumor was excised, and the patient underwent laparoscopic partial nephrectomy. Typical features of renal oncocytoma were observed upon histopathological examination of the resected specimen. The patient was catheterized, and bladder irrigation with clot retraction was performed.

A Nonsense Mitochondrial DNA Mutation Associates with Dysfunction of HIF1α in a Von Hippel-Lindau Renal Oncocytoma

The Von Hippel-Lindau (VHL) syndrome has been rarely associated with renal oncocytomas, and tumors usually show HIF1α chronic stabilization. By contrast, oncocytomas mainly associated with respiratory chain (RC) defects due to severe mitochondrial DNA (mtDNA) mutations are incapable of stabilizing HIF1α, since oxygen consumption by the RC is dramatically diminished and prolylhydroxylase activity is increased by α-ketoglutarate accumulation following Krebs cycle slowdown. Here, we investigate the cooccurrence of a pseudohypoxic condition with oncocytic transformation in a case of VHL-associated renal oncocytoma. While HIF1α was abundant in nuclei concordantly with defects in VHL, negative staining of its targets carbonic anhydrase IX (CAIX) and glucose transporter GLUT1, usually overexpressed in VHL-associated neoplasms, suggested HIF1α to be present in its inactive (hydroxylated) form. MtDNA sequencing and immunohistochemistry analyses revealed a MT-CO1 stop-gain mutation and cytochrome c oxidase loss. We suggest that a mitochondrial respiration impairment may lead to hyperhydroxylation of the transcription factor, which we confirmed by specific staining of hydroxylated HIF1α. Such inactive form hence accumulated in the VHL-deficient tumor, where it may contribute to the benign nature of the neoplasm. We propose that the protumorigenic role of HIF1α in VHL cancers may be blunted through drugs inhibiting mitochondrial respiratory complexes, such as metformin.

Emerging entities in renal cell neoplasia: thyroid-like follicular renal cell carcinoma and multifocal oncocytoma-like tumours associated with oncocytosis

The list of accepted entities of renal cell neoplasia has burgeoned since the turn of the century through recognition of rare tumour types and the discovery of genetic mutations driving renal neoplasia syndromes. This growth has not finished and in this report we present examples of each of these types which were not included in the 2016 World Health Organization classification of renal neoplasia, but are candidates for inclusion in the next edition of the classification. Thyroid-like follicular renal cell carcinoma is a rare tumour type with a distinctive microscopic appearance resembling follicles of the thyroid gland. Thirty-nine cases have been described and the findings have been reasonably consistent. Oncocytoma-like tumours associated with oncocytosis arise as a result of somatic mutations in the mitochondrial genome. The differential diagnosis is mainly with the renal lesions of the Birt-Hogg-Dubé syndrome, which is the result of germline mutations in the folliculin gene. Patients with oncocytoma-like tumours associated with oncocytosis are at great risk of developing renal failure as the proliferating lesions replace the renal parenchyma. Oncocytoma-like tumours have never been found to metastasise.

Etiopathogenesis of oncocytomas

Oncocytomas are distinct tumors characterized by an abnormal accumulation of defective and (most probably) dysfunctional mitochondria in cell cytoplasm of such tumors. This particular phenotype has been studied for the last decades and the clarification of the etiopathogenic causes are still needed. Several mechanisms involved in the formation and maintenance of oncocytomas are accepted as reasonable causes, but the relevance and contribution of each one for oncocytic transformation may depend on different cancer etiopathogenic contexts. In this review, we describe the current knowledge of the etiopathogenic events that may lead to oncocytic transformation and discuss their contribution for tumor progression and mitochondrial accumulation.

An 11-bp duplication in the promoter region of the VHL gene in a patient with cerebellar hemangioblastoma and renal oncocytoma

Central nervous system hemangioblastomas are benign vascular tumours that may present sporadically or as manifestation of the von Hippel-Lindau (VHL) disease. VHL Syndrome is a rare autosomal dominant disorder characterized, besides hemangioblastomas, by susceptibility to multifocal and bilateral renal cell carcinoma and cysts, retinal angiomas, pheochromocytoma, epididymis cystoadenoma, pancreatic cysts and/or islet cell tumours. Germline mutations of VHL tumour suppressor gene cause the VHL disease, while somatic mutations have been associated with sporadic hemangioblastomas and clear-cell renal carcinomas. We identified an 11-bp duplication in the promoter region of the VHL gene in a VHL-affected individual. Functional analysis revealed that this variant affects the binding or the binding affinity of one or more transcription factors that regulate the transcription of VHL in vivo, reducing the endogenous levels of VHL mRNA. Moreover, consistent with the "two hits" model, microsatellite analysis of hemangioblastoma tissue from this patient revealed Allelic Imbalance for the chromosomal region near the VHL gene. We propose that these molecular events, through a loss of pVHL function, lead to the onset of the VHL-related tumours in that individual.