Gillian Stearns, MD
Oleg Shapiro, MD, FACS
BASICS
DESCRIPTION
• Renal oncocytoma is the most common benign solid renal tumor in adults
• Usually asymptomatic at time of presentation
• Frequently detected incidentally at time of CT scan
EPIDEMIOLOGY
Incidence
• 3–7% of all renal masses
• Epidemiology similar to renal cell carcinoma (RCC)
• Male > female (2:1)
• Median age of diagnosis 62 yr
• 6% occur bilaterally
• 17% multifocal
Prevalence
N/A
RISK FACTORS
• Familial renal oncocytoma syndrome
– Described rarely to date
• Birt–Hogg–Dubé (BHD)
Genetics
• Most frequent abnormalities (1,2):
– Loss of chromosome 1p
– Loss of chromosome Y (males)
• Less frequent translocations
– Breakpoint region on 11q13
– Region encoding mDNA
– Loss of heterozygosity at chromosomes 1,14,21
May reflect progression of oncocytoma to chromophobe RCC
PATHOPHYSIOLOGY
• Arise from intercalated cells in collecting duct of kidney (like chromophobe RCC)
• Occasionally oncocytoma and RCC may be found in the same kidney
ASSOCIATED CONDITIONS
• Most usually sporadic
• BHD
– Autosomal dominant
– Mutation in gene for folliculin
– Renal tumors
Chromophobe/oncocytoma
– Spontaneous pneumothorax, lung cysts
– Fibrofolliculomas, especially on face
GENERAL PREVENTION
No preventative strategies have been described. Relatives of those with genetic syndromes may be screened.
DIAGNOSIS
HISTORY
• Most patients asymptomatic
• Incidentally detected
• Gross hematuria/flank pain/flank mass rare
• Family history of renal tumors, fibrofolliculomas, lung cysts/pneumothorax—rule out BHD
PHYSICAL EXAM
• No specific findings for sporadic oncocytoma
• Palpable flank mass rare
• Dermatologic exam if suspected BHD
DIAGNOSTIC TESTS & INTERPRETATION
Lab
• No lab test can identify renal tumor as oncocytoma
• Lab panel as with any newly diagnosed renal mass
– CBC, chemistry panel, LFTs
Imaging
• Cannot be used to reliably distinguish oncocytoma from RCC
• CT with and without IV contrast
– Diagnostic test of choice for solid renal mass
– Central scar within mass often seen in oncocytoma, but this can be confused with necrosis, commonly seen with RCC
• MRI
– Solid enhancing renal mass ± central scar
– Test of choice with IV contrast allergy, renal insufficiency
• Renal US
– Not typically helpful for identification of mass as oncocytoma
• Renal angiogram
– Spoke wheel pattern of feeding vessels
Not definitive for diagnosis
– Usually not helpful in evaluation of renal mass
• Metastatic evaluation for solid renal mass
– Chest x-ray vs. chest CT
• Additional studies may be indicated clinically
Diagnostic Procedures/Surgery
• Percutaneous biopsy
– May be useful to exclude metastasis to kidney based on patient history
– May guide management of poor surgical candidates
• Pitfalls of biopsy
– Difficult to distinguish oncocytoma from chromophobe RCC
– Coexistence of RCC and oncocytoma in up to 10% cases
Pathological-Findings (3,4)
• The term “oncocytoma” is a general descriptor of an epithelial tumor that consists of oncocytes. Oncocytes are large eosinophilic cells with small, round, benign-appearing nuclei without nucleoli.
– Oncocytomas can arise in a number of different organs
• Renal oncocytoma: Gross findings
– Well-circumscribed mass, mahogany brown, often with pseudocapsule
– Average size 6–7 cm
– 33% with central stellate scar
– 20% demonstrate extension into perinephric fat
– Calcifications and necrosis rarely seen
• Renal oncocytoma: Microscopic findings
– Round to polygonal eosinophilic cells
– Abundance of mitochondria seen on electron microscopy
– Mitotic figures rare
– Regular nuclei
– Cells arranged in distinct nests
– May be difficult to distinguish from chromophobe RCC
Colloidal iron stain positive in chromophobe RCC but not oncocytoma
Chromophobe RCC is vimentin, cytokeratin 7 positive
CD82 and epithelial-related antigen (MOC31) may be helpful in the distinction between chromophobe RCC and renal oncocytoma
Gene expression differences are being explored
The World Health Organization (2004) renal tumor classification indicates renal oncocytomas are benign neoplasms. In the past some renal oncocytomas were classified as malignant.
This may have resulted from confusion with clear cell renal carcinomas with eosinophilic component or due to eosinophilic chromophobe RCC (low metastatic potential)
ALERT
Although oncocytoma has “Classic Findings” on imaging, no radiographic studies exist to differentiate benign oncocytoma from malignant RCC.
DIFFERENTIAL DIAGNOSIS
• Adrenal mass
• Angiomyolipoma
• Carcinoid tumor
• Collecting duct tumor
• Cystic nephroma
• Cysts
• Focal pyelonephritis
• Hemangioma
• Inflammatory masses (xanthogranulomatous pyelonephritis (XGP), abscess)
• Leiomyoma
• Metanephric adenoma
• Metastasis
• Pseudotumor (column of Bertin)
• RCC
• Renal cortical adenoma
• Renal lymphoma
• Renal medullary carcinoma
• Renal sarcoma
• Reninoma
• Urothelial carcinoma
• Wilms tumor
TREATMENT
GENERAL MEASURES
Mainstay of treatment is surgical
MEDICATION
First Line
No medical treatment exists
Second Line
N/A
SURGERY/OTHER PROCEDURES
• Establishes diagnosis of oncocytoma
• Partial nephrectomy whenever feasible based on size and location
• Radical nephrectomy rarely indicated unless very large, uncertain diagnosis or partial not possible
ADDITIONAL TREATMENT
Radiation Therapy
No role
Additional Therapies
N/A
Complementary & Alternative Therapies
• Renal cryotherapy and radiofrequency ablation (5)
– Being studied as treatment option
– Unable to differentiate between oncocytoma and RCC due to lack of tissue for histology
– Primarily for smaller lesions (<3 cm)
– May be done laparoscopically or percutaneously
– No long-term follow-up exists
– Usually considered for poor surgical candidates
• Active surveillance
– Good for select patients with solid renal masses, but no size can reliably differentiate between benign and malignant processes
3 cm usually used as cutoff in BHD
ONGOING CARE
PROGNOSIS
• Oncocytoma is uniformly considered a benign tumor and surgical removal is curative
• Multiple series report no metastases or death from oncocytoma on long-term follow-up
• Older, rare reports of metastases may represent unrecognized, low-grade RCC (6,7)
• Risk of metachronous oncocytoma 4–6%
COMPLICATIONS
• Perioperative for partial/radical nephrectomy
– Bleeding, infection, urine leak
• Long term after nephrectomy depends on renal reserve
– Chronic renal insufficiency/dialysis
FOLLOW-UP
Patient Monitoring
• Patient monitoring
– Long-term surveillance of renal units recommended annually to semiannually
– Metachronous ipsilateral and bilateral oncocytomas have been reported
• Renal US preferred modality
– Minimizes radiation exposure
– No need for IV contrast
• Urinalysis
– Hematuria/proteinuria
• Serum creatinine
Patient Resources
• Kidney Cancer Association
www.kidneycancer.org/
REFERENCES
1. Al-Saleem T, Cairns P, Dulaimi EA, et al. The genetics of renal oncocytosis: A possible model for neoplastic progression. Cancer Genet Cytogenet. 2004;152:23–28.
2. Boris RS, Benhammou J, Merino M, et al. The impact of germline BHD mutation on histological concordance and clinical treatment of patients with bilateral renal masses and known unilateral oncocytoma. J Urol. 2011;185(6):2050–2055.
3. Gudbjartsson T, Hardarson S, Petursdottir V, et al. Renal oncocytoma: A clinicopathological analysis of 45 consecutive cases. BJU Int. 2005;96:1275–1279.
4. Kuroda N, Tanaka A, Ohe C, et al. Review of renal oncocytosis (multiple oncocytic lesions) with focus on clinical and pathobiological aspects. Histol Histopathol. 2012;27(11):1407–1412.
5. Breen DJ, Bryant TJ, Abbas A, et al. Percutaneous cryoablation of renal tumours: Outcomes from 171 tumours in 147 patients. BJU Int. 2013;112(6):758–765.
6. Romis L, Cindolo L, Patard JJ, et al. Frequency, clinical presentation, and evolution of renal oncocytomas: Multicentric experience from a european database. Eur Urol. 2004;45:53–57.
7. Van der Kwast T, Perez-Ordoñez B. Renal oncocytoma, yet another tumour that does not fit in the dualistic benign/malignant paradigm. J Clin Pathol. 2007;60(6):585–586.
ADDITIONAL READING
• Chen YT, Tu JJ, Kao J, et al. Messenger RNA expression ratios among 4 genes predict subtypes of renal cell carcinoma and distinguish oncocytoma from carcinoma. Clin Cancer Res. 2005;11:6558–6566.
• Dechet CB, Bostwick DG, Blute ML, et al. Renal oncocytoma: Multifocality, bilateralism, metachronous tumor development and coexistent renal cell carcinoma. J Urol. 1999;162:40–42.
• Linehan WM, Walther MM, Zbar B. The genetic basis of cancer of the kidney. J Urol. 2003;170:2163–2172.
See Also (Topic, Algorithm, Media)
• BHD
• Reference Tables: TNM: Kidney Cancer
• Renal Cell Carcinoma, Chromophobe
• Renal Cell Carcinoma, General Considerations
• Renal Mass, Algorithm 
• Renal Mass, Intraoperative Consultation
• Renal Masses, Benign WHO, Classification
• Renal Oncocytoma Image 
• Renal Pseudotumors
CODES
ICD9
223.0 Benign neoplasm of kidney, except pelvis
ICD10
• D30.00 Benign neoplasm of unspecified kidney
• D30.01 Benign neoplasm of right kidney
• D30.02 Benign neoplasm of left kidney
CLINICAL/SURGICAL PEARLS
• Oncocytoma is a benign solid renal lesion.
• No imaging study reliably differentiates oncocytoma from RCC. The CT finding of a central scar, previously felt to be specific for oncocytoma, has been found with RCCs, and this finding is not specific.