Renal Oncocytoma: A Benign Kidney Cancer

By Chris

Renal Oncocytoma is a type of kidney cancer. Unlike most other kidney cancers that can grow uncontrollably and spread to other parts of the body, renal oncocytomas typically remain localized and do not metastasize. Therefore, distinguishing between malignant and benign tumors, like renal oncocytoma, is crucial for determining the appropriate course of treatment and for patient prognosis.

Renal Oncocytoma
Renal Oncocytoma is a type of kidney cancer. Unlike most other kidney cancers that can grow uncontrollably and spread to other parts of the body, renal oncocytomas typically remain localized and do not metastasize. This is how renal oncocytoma looks under a microscope. Image Source. 

How Common is Renal Oncocytoma

Renal Oncocytoma is a relatively rare condition, representing about 3 to 7% of renal neoplasms. This benign kidney tumor is more commonly diagnosed in middle-aged and older adults, with a slight predominance in men compared to women. Renal oncocytomas rarely occur in children.

Risk Factors for Renal Oncocytoma

There are no risk factors specific to renal oncocytoma. Being a rare type of kidney cancer, the general risk factors for kidney cancer also apply to renal oncocytoma. One of the most significant risk factors for renal oncocytoma is age, as this condition is more commonly diagnosed in individuals who are middle-aged and older, particularly those in their 60s and 70s. 

In addition to age, gender plays a crucial role, with men being slightly more likely to develop renal oncocytoma compared to women. Other risk factors include smoking, obesity, hypertension, and exposure to certain chemicals.

Genetic Syndromes and Renal Oncocytoma

Genetic syndromes such as Birt–Hogg–Dubé (BHD) syndrome and Tuberous sclerosis complex are associated with an increased risk of renal oncocytomas, and the risk for multiple and bilateral disease is greater compared to the general population. 

Birt–Hogg–Dubé syndrome is an inherited autosomal dominant disease, where just one affected gene from a parent can cause the syndrome in their child. Patients with Birt–Hogg–Dubé syndrome typically develop fibrofolliculomas, lung cysts, and are at increased risk of developing renal oncocytomas, which may be focal or bilateral. 

Tuberous sclerosis complex, also an autosomal dominant syndrome, predisposes patients to various lesions. Although rare, individuals with tuberous sclerosis complex have an increased risk of developing bilateral or multifocal renal oncocytomas.

Symptoms and Diagnosis of Renal Oncocytoma

There are no symptoms or diagnostic criteria specific to renal oncocytoma. Most cases of renal oncocytoma are diagnosed incidentally when patients undergo imaging for other reasons. Being a type of kidney cancer, the general symptoms and diagnosis applicable to kidney cancer also apply to renal oncocytoma. 

This means, in early stages, it usually does not show any symptoms, and in advanced stages, it could produce non-specific symptoms such as blood in the urine (hematuria), flank pain, and a palpable mass. Diagnosis is typically made through imaging and biopsy.

Diagnostic Challenge of Renal Oncocytoma

A major diagnostic challenge with renal oncocytoma is its similarity to chromophobe renal cell carcinoma, another type of kidney cancer. Morphologically, both renal oncocytoma and chromophobe renal cell carcinoma appear almost identical when observed via imaging, presenting a diagnostic challenge. This distinction is critical because chromophobe renal cell carcinoma can metastasize, while renal oncocytoma is benign and does not spread. 

Currently, biopsy is the only method to accurately diagnose, performed either before surgical removal of the kidney (nephrectomy) or as part of the surgical process. The dilemma is that since renal oncocytoma is benign, it might not require any treatment. However, if it is chromophobe renal cell carcinoma, surgical removal is necessary due to its potential to spread. The inability to distinguish between the two with 100% accuracy from radiological imaging leads to unnecessary surgery for many patients with renal oncocytoma.

Morphology and Pathology of Renal Oncocytoma

Renal oncocytoma is characterized by its unique cellular structure and appearance. It typically presents as a well-circumscribed, round mass, often encapsulated by a fibrous capsule, with a mahogany brown color and a central scar. Microscopically, it is made up of oncocytes - large cells with abundant granular, eosinophilic cytoplasm due to high mitochondrial content, and round nuclei with prominent nucleoli. 

These cells are arranged in a compact, nested, or tubular pattern, creating a distinctive appearance that aids pathologists in identifying this tumor. Limited evidence suggests that the pathology of renal oncocytoma is linked to chromosomal abnormalities, including the loss of chromosome 1, loss of the Y chromosome, and rearrangement of the 11q13 region of the chromosome.

Treatment of Renal Oncocytoma

Since renal oncocytomas typically do not behave as aggressively as malignant kidney cancers, the treatment strategy often involves active surveillance, especially for small, asymptomatic tumors. This approach allows doctors to monitor the tumor closely without immediate intervention, minimizing the risks associated with surgery. 

For tumors that are large, symptomatic, or showing signs of growth, surgical removal is the preferred option. Techniques such as partial nephrectomy, where only the tumor and a small margin of healthy tissue are removed, or radical nephrectomy, which involves the removal of the entire kidney, are determined based on the tumor's size and location. Unlike treatments for malignant tumors, the benign nature of renal oncocytoma typically excludes the need for chemotherapy or radiation therapy. 

Post-treatment, patients undergo regular follow-ups to monitor for any changes that might indicate the need for further intervention, ensuring the long-term health and well-being of the patient.

Metastatic Renal Oncocytoma

Although renal oncocytoma is generally considered a benign neoplasm, there have been suggestions that it might metastasize. However, these reports are thought to be biased, with the cases most likely being chromophobe renal cell carcinomas instead. The current consensus is that metastatic renal oncocytoma is extremely rare.

Prognosis of Renal Oncocytoma

The prognosis for renal oncocytoma is generally excellent, given its benign nature and the low likelihood of spreading or becoming malignant. Unlike renal cell carcinoma, which is cancerous and can pose significant health risks, renal oncocytoma usually does not invade surrounding tissues or metastasize to other parts of the body. With proper diagnosis and appropriate management, individuals diagnosed with renal oncocytoma can expect a normal life expectancy.

References

  1. Trevisani F. et al. Renal Oncocytoma: The Diagnostic Challenge to Unmask the Double of Renal Cancer. Int J Mol Sci. 2022 Mar; 23(5): 2603.
  2. Williams GM et al. Renal Oncocytoma. StatPearls.

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