Renal oncocytosis

Morphological and Molecular Study of Hybrid Oncocytic/Chromophobe Tumor of the Kidney Associated with Sporadic Renal Oncocytosis and Chronic B-Cell Lymphocytic Leukemia: The Possible Contribution of Lymphoma to Renal Oncocytosis

Hybrid oncocytic/chromophobe tumor (HOCT) of the kidney arising from a precursor oncocytosis not associated with the Birt-Hogg-Dubé (BHD) syndrome is an unusual and highly interesting neoplasm. Immunohistochemical and molecular findings suggest that HOCT is an entity distinct from both oncocytoma and chromophobe carcinoma. Although uncertainty persists regarding the factors predisposing to the development of HOCT, experimental findings suggest that it may arise due to the effect of toxins or in association with chronic kidney failure. The potential role of prior renal lymphoma in the development of oncocytosis has not hitherto been examined. We present a morphological, immunohistochemical, and molecular analysis of an HOCT arising from renal oncocytosis in conjunction with CLL affecting the kidney. The findings suggest that this tumor belongs to a family of similar neoplasms including oncocytoma, the eosinophilic variant of chromophobe renal-cell carcinoma (CRCC), and low-grade oncocytic tumor, even though these neoplasms may arise from different precursor lesions. HOCT and oncocytosis revealed the same immunohistochemical profile consistent on positivity for epithelial membrane antigen (EMA), cytokeratin 7 (Ck7), E-cadherin, CAM 5.2 and negativity for Pax-8, vimentin, renal-cell carcinoma (RCC) antigen, CD117, racemase, progesterone receptor, and CD10. The Ki-67 proliferation index was <1%. Molecular analysis of the tumor revealed the AKT3 gene mutation variant, classified as probably pathogenic, together with FOS1 gene amplification and no copy number variations (CNVs). Finally, we present a case of HOCT arising from a nonhereditary renal oncocytosis in conjunction with B lymphoma that raises interesting questions regarding pathogenesis.

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.

Birt-Hogg-Dubé syndrome: Clinical and molecular aspects of recently identified kidney cancer syndrome

Birt-Hogg-Dubé syndrome is an autosomal dominantly inherited disease that predisposes patients to develop fibrofolliculoma, lung cysts and bilateral multifocal renal tumors, histologically hybrid oncocytic/chromophobe tumors, chromophobe renal cell carcinoma, oncocytoma, papillary renal cell carcinoma and clear cell renal cell carcinoma. The predominant forms of Birt-Hogg-Dubé syndrome-associated renal tumors, hybrid oncocytic/chromophobe tumors and chromophobe renal cell carcinoma are typically less aggressive, and a therapeutic principle for these tumors is a surgical removal with nephron-sparing. The timing of surgery is the most critical element for postoperative renal function, which is one of the important prognostic factors for Birt-Hogg-Dubé syndrome patients. The folliculin gene (FLCN) that is responsible for Birt-Hogg-Dubé syndrome was isolated as a novel tumor suppressor for kidney cancer. Recent studies using murine models for FLCN, a protein encoded by the FLCN gene, and its two binding partners, folliculin-interacting protein 1 (FNIP1) and folliculin-interacting protein 2 (FNIP2), have uncovered important roles for FLCN, FNIP1 and FNIP2 in cell metabolism, which include AMP-activated protein kinase-mediated energy sensing, Ppargc1a-driven mitochondrial oxidative phosphorylation and mTORC1-dependent cell proliferation. Birt-Hogg-Dubé syndrome is a hereditary hamartoma syndrome, which is triggered by metabolic alterations under a functional loss of FLCN/FNIP1/FNIP2 complex, a critical regulator of kidney cell proliferation rate; a mechanistic insight into the FLCN/FNIP1/FNIP2 pathway could provide us a basis for developing new therapeutics for kidney cancer.

Distal nephron neoplasms

Tumours of the distal nephron are uncommon but can create diagnostic difficulties. They may be divided into three groups-tumours of intercalated cell phenotype, those of principal cell phenotype and others with an unconfirmed distal nephron origin. Oncocytomas, chromophobe carcinoma and hybrid oncocytoma chromophobe carcinoma, all show features of intercalated cells and the distinction amongst these is one of the most common areas of diagnostic dilemma. Collecting duct carcinoma and renal medullary carcinoma are the most aggressive forms of renal cancer but recent evidence suggests they may respond to targeted therapy so their recognition becomes crucial to the management of these patients. There remains debate over the precise phenotype of both tubulocystic carcinoma and mucinous tubular and spindle cell carcinoma.

Unilateral renal oncocytosis and combined hybrid tumor: a case report and review of the literature

Renal oncocytosis is a very rare cause of multiple renal masses. Imaging features of renal oncocytosis and combined tumors have rarely been reported. Here, we describe a case of unilateral left renal oncocytosis and a combined hybrid tumor between chromophobe renal cell carcinoma and oncocytoma, which were depicted on CT and MR imaging as multiple enhancing solid masses with one dominant mass. Additionally, we reviewed the literature.

Two Japanese cases of birt-hogg-dubé syndrome with pulmonary cysts, fibrofolliculomas, and renal cell carcinomas

Birt-Hogg-Dubé syndrome (BHD) is a rare autosomal dominant inherited disease caused by a germline mutation in the folliculin gene mapped in the region of chromosome 17p11.2. BHD predisposes the patient to cutaneous fibrofolliculomas (FFs), pulmonary cysts (PCs), and renal cell carcinoma (RC). Here, we present two cases of BHD in Japanese patients. One patient was a 37-year-old female, and the other a 35-year-old male. Each of the patients was affected by all three symptoms of BHD. Both patients had unremarkable FFs, asymptomatic PCs, and asymptomatic RC. The presence of RC was revealed by abdominal ultrasonic examination. We also summarized the data from 62 Asian cases of BHD from the available literature and found that their FFs were unremarkable. In addition, the proportion of BHD patients with FF is smaller for Asian patients than it is for Caucasian patients. We also found that it is rare for BHD patients in Asia to show all three symptoms of BHD. Careful inspection of the skin as well as skin biopsies are important for the early detection of BHD cases in Asia.

Regulation of mitochondrial oxidative metabolism by tumor suppressor FLCN

BACKGROUND

Birt-Hogg-Dubé (BHD) syndrome is a hereditary hamartoma syndrome that predisposes patients to develop hair follicle tumors, lung cysts, and kidney cancer. Genetic studies of BHD patients have uncovered the causative gene, FLCN, but its function is incompletely understood.

METHODS

Mice with conditional alleles of FLCN and/or peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PPARGC1A), a transcriptional coactivator that regulates mitochondrial biogenesis, were crossbred with mice harboring either muscle creatine kinase (CKM) -Cre or myogenin (MYOG) -Cre transgenes to knock out FLCN and/or PPARGC1A in muscle, or cadherin 16 (CDH16)- Cre transgenes to knock out FLCN and/or PPARGC1A in kidney. Real-time polymerase chain reaction, immunoblotting, electron microscopy, and metabolic profiling assay were performed to evaluate mitochondrial biogenesis and function in muscle. Immunoblotting, electron microscopy, and histological analysis were used to investigate expression and the pathological role of PPARGC1A in FLCN-deficient kidney. Real-time polymerase chain reaction, oxygen consumption measurement, and flow cytometry were carried out using a FLCN-null kidney cancer cell line. All statistical analyses were two-sided.

RESULTS

Muscle-targeted FLCN knockout mice underwent a pronounced metabolic shift toward oxidative phosphorylation, including increased mitochondrial biogenesis (FLCN ( f/f ) vs FLCN ( f/f ) /CKM-Cre: % mitochondrial area mean = 7.8% vs 17.8%; difference = 10.0%; 95% confidence interval = 5.7% to 14.3%; P < .001), and the observed increase in mitochondrial biogenesis was PPARGC1A dependent. Reconstitution of FLCN-null kidney cancer cells with wild-type FLCN suppressed mitochondrial metabolism and PPARGC1A expression. Kidney-targeted PPARGC1A inactivation partially rescued the enlarged kidney phenotype and abrogated the hyperplastic cells observed in the FLCN-deficient kidney.

CONCLUSION

FLCN deficiency and subsequent increased PPARGC1A expression result in increased mitochondrial function and oxidative metabolism as the source of cellular energy, which may give FLCN-null kidney cells a growth advantage and drive hyperplastic transformation.

Renal oncocytosis: management and clinical outcomes

PURPOSE

Renal oncocytosis is a rare pathological condition in which renal parenchyma is diffusely involved by numerous oncocytic nodules in addition to showing a spectrum of other oncocytic changes. We describe our experience with renal oncocytosis, focusing on management and outcomes.

MATERIALS AND METHODS

A total of 20 patients with a final pathological diagnosis of renal oncocytosis from July 1995 through June 2009 were included in the analysis. Patient demographics, intraoperative variables and postoperative outcomes are reported.

RESULTS

Median age at nephrectomy was 71 years (IQR 59-75). Of the patients 15 (75%) had bilateral disease. There were 23 operations (9 right side, 14 left side) performed on 20 patients, and of these procedures 13 (57%) were partial nephrectomies and 10 (43%) were radical nephrectomies. Median dominant tumor mass diameter was 4.1 cm (IQR 3-6.4, range 1 to 14.6). The most common dominant tumor histology was hybrid tumor between oncocytoma and chromophobe renal cell carcinoma in 13 of 23 specimens (57%), followed by chromophobe renal cell carcinoma in 6 (26%), oncocytoma in 3 (13%) and conventional renal cell carcinoma in 1 (4%). Ten patients (50%) had preexisting chronic kidney disease before nephrectomy and chronic kidney disease developed in 5 more after surgery. After a median followup of 35 months no patients had metastatic disease.

CONCLUSIONS

Patients with renal oncocytosis usually present with multiple and bilateral renal nodules. Half of the patients had chronic kidney disease at diagnosis and 25% had new onset of chronic kidney disease. No patient had distant metastatic disease during followup. Our management approach is to perform partial nephrectomy when possible and then use careful surveillance of the remaining renal masses.

Sporadic hybrid oncocytic/chromophobe tumor of the kidney: a clinicopathologic, histomorphologic, immunohistochemical, ultrastructural, and molecular cytogenetic study of 14 cases

Hybrid oncocytic/chromophobe tumors (HOCT) of the kidney have been described in patients with Birt-Hogg-Dubé syndrome (BHD) and in association with renal oncocytosis without BHD. HOCT in patients without evidence of BHD or renal oncocytosis is exceedingly rare, and these cases have been poorly characterized. We have identified and studied 14 cases of HOCT from previously diagnosed renal oncocytomas (398 cases) and chromophobe renal cell carcinomas (351 cases) without evidence of BHD or renal oncocytosis. Immunohistochemical, ultrastructural, and molecular genetic studies analyzing numerical chromosomal changes, loss of heterozygosity for chromosome 3p, and mutation status of VHL, c-kit, PDGFR, and folliculin (FLCN) genes were performed. HOCTs were identified in nine men and five women (age range 40-79 years). The size of tumors ranged from 2 to 11 cm. All tumors displayed a solid alveolar architecture and were composed of cells with abundant granular eosinophilic oncocytic cytoplasm with perinuclear halos. Occasional binucleated neoplastic cells were present, but irregular, hyperchromatic, wrinkled (raisinoid) nuclei were absent. The cytoplasm contained numerous mitochondria of varying sizes, but only sparse microvesicles with amorphic lamellar content were found. Tumors were positive for CK7 (12/14), AE1-AE3 (14/14), anti-mitochondrial antigen (14/14), E-cadherin (11/13), parvalbumin (12/14), and epithelial membrane antigen (14/14). Tumors were generally negative for racemase, CK20, CD10, and carboanhydrase IX. Interphase fluorescence in situ hybridization revealed multiple chromosomal losses and gains with a median of four (range 1-9) chromosomal aberrations per case. Monosomy of chromosome 20 was common and found in 7 of 14 cases. Monosomy of chromosomes 6 and 9 was present in 4 of 14 cases each, of which two cases displayed monosomy for both chromosomes 6 and 9. Polysomy of chromosomes 10, 21, and 22 was found in 4/14 cases each, of which one case displayed polysomy for all these three chromosomes. No pathogenic mutations were found in the VHL, c-kit, PDGFR, and folliculin (FLCN) genes. (1) We have shown that hybrid oncocytic/chromophobe tumors of the kidney do occur, albeit rarely, outside the Birt-Hogg-Dubé syndrome and without associated renal oncocytosis. (2) These tumors constitute a relatively homogenous group with histomorphologic features of both chromophobe renal cell carcinoma and renal oncocytoma. (3) Sporadic hybrid oncocytic/chromophobe renal tumors are characterized by multiple numerical aberrations (both mono- and polysomies) of chromosomes 1, 2, 6, 9, 10, 13, 17, 21, and 22 and lack of mutations in the VHL, c-kit, PDGFRA, and FLCN genes. (4) The tumors seem to behave indolently as no evidence of malignant behavior was documented in our series, although admittedly, the follow-up was too short to fully elucidate the biological nature of this rare neoplasm. At worst, these tumors could have a low malignant potential, which only can be found out with longer follow-up.

Renal oncocytosis: imaging considerations

Renal oncocytosis is a very rare entity. Although it has been described in pathology and surgery literature, the imaging findings of renal oncocytosis have not yet been described in the radiology literature. We present three cases of renal oncocytosis. The imaging features and clinical considerations are discussed.

Diffuse minute clear cell proliferation in kidney: case report and review of literature

To our knowledge, diffuse involvement of renal parenchyma by multiple minute foci of clear cell proliferations has not been previously reported. We report such a case, found incidentally, in an 86-year-old woman who had undergone right ureteronephrectomy for pyeloureteral urothelial carcinoma. Macroscopy of the kidney showed numerous yellow dot-like cortical nodules less than 0.3 cm. Histologic examination of the kidney and nodules revealed innumerable foci of minute clear cell proliferations in a background of chronic pyelonephritis. The benign or malignant nature of those clear cell microtumors was investigated by immunohistochemistry and fluorescent in situ hybridization analysis of chromosome 3p.

Interphase cytogenetic analysis with centromeric probes for chromosomes 1, 2, 6, 10, and 17 in 11 tumors from a patient with bilateral renal oncocytosis

Renal oncocytosis is characterized by the presence of multiple tumors with oncocytic features, often associated with small clusters of tubule-like structures with oncocytic change. The morphologic features of the oncocytic nodules encompass a spectrum of appearances, with patterns typical of renal oncocytoma or classic chromophobe renal cell carcinoma, as well as 'hybrid' tumors with features resembling both oncocytoma and chromophobe renal cell carcinoma. We utilized interphase cytogenetic methods to study 11 tumors from the kidneys of a 45-year-old woman. The tumors included morphologically classical oncocytomas and 'hybrid' tumors with features reminiscent of chromophobe carcinoma. The kidneys also showed foci of oncocytic change in renal tubules. Fluorescence in situ hybridization was performed with centromeric probes for chromosomes 1, 2, 6, 10, and 17 in each of the 11 tumors to determine whether or not there were losses of the chromosomes that are most frequently lost in chromophobe renal cell carcinomas. Neoplastic nuclei from each tumor were evaluated for the number of hybridization signals and scored according to the percentage of nuclei with one, two, and three or more signals. The normal renal parenchyma surrounding the tumors was used as control tissue. All 11 tumors from this patient with renal oncocytosis showed no loss of any of the chromosomes 1, 2, 6, 10, or 17, a pattern identical to that found in normal control tissues. These observations weigh against the concept that hybrid tumors of oncocytosis are closely related to chromophobe renal cell carcinoma.

Identification and characterization of Birt-Hogg-Dubé associated renal carcinoma

The Birt-Hogg-Dubé (BHD) gene is responsible for BHD syndrome, a rare autosomal dominant disease, characterized by benign hair follicle tumours, spontaneous pneumothorax and renal neoplasms with diverse histology. To elucidate its involvement in the development of renal neoplasms, we examined a total of 100 sporadic renal tumours with various histological subtypes for BHD mutation by SSCP-sequencing analyses. We found one germline insertion mutation in the C8 hotspot of exon 11 (c.1733insC), which is known to have a strong association with renal tumour occurrence. The germline-mutated patient suffered from solitary renal cell carcinoma (RCC) but did not have any other BHD manifestations or family history. The tumour revealed heterogeneous cytomorphology, mainly a mixture of eosinophilic and focally clear cells with tubulopapillary architecture. In this tumour, both BHD alleles were inactivated by germline mutation concomitant with loss of heterozygosity, and the amount of BHD mRNA detected by real-time quantitative PCR (RQ-PCR) was very low. Renal tumour subtype/nephron segment-specific gene expression detected by RQ-PCR demonstrated that the tumour expressed relatively high amounts of alpha-methylacyl-CoA racemase (AMACR) and the KIT oncogene, but relatively low amounts of carbonic anhydrase IX (CA9), aquaporin 1 (AQP1), claudin 7 (CLDN7), parvalbumin (PVALB), chloride channel Kb (CLCNKB) and 11-beta-hydroxysteroid dehydrogenase 2 (HSD11B2), suggesting diverse mRNA signatures. Further clustering analysis of 88 renal tumours based on expression of these eight genes sub-classified the tumour as close to oncocytomas and chromophobe RCCs, which are considered distal nephron-associated tumours. These data suggest that somatic mutation of BHD is relatively rare in Japanese patients. The BHD-mutated RCC identified in this study, which exhibits heterogeneous biological features in both morphology and gene expression signatures, seems to deviate from our current understanding of renal tumour classification.