Renal oncocytoma is a non-cancerous growth in the kidney with a special appearance under the microscope. Unlike kidney cancers, it rarely causes urinary symptoms and is often detected incidentally in a scan. The outcome for renal oncocytoma is good with options to monitor or remove by surgery.

Kidney lesions or growths can be cancerous or non-cancerous. Their names depend mostly on their microscopic appearance. The name oncocytic means cells with a pink, plump appearance. Oncocytoma is a non-cancerous growth or in other words a benign lesion. It is known to occur in the outer part of the kidney called the cortex.¹ Often detected incidentally in a scan, renal oncocytomas have very good outcomes meaning they don't spread or grow aggressively.

Oncocytic means a microscopic appearance that shows plump, pink cells. Other possibilities for kidney tumours with this appearance include:

• Renal oncocytosis 
• Chromophobe carcinoma
• Low grade oncocytic tumors which is a recent category in WHO kidney tumour categorisation

Renal oncocytomas is said to make up about 3 to 7 percent of renal epithelial tumours,² meaning tumours arising from surface lining type of cells.

Who can get renal oncocytoma?

Renal oncocytomas can occur at any age in adults. But the commonest age at which it occurs is reported to be 60 years.¹

They seem to occur more commonly in those who are assigned male at birth (AMAB) compared to those who are assigned female at birth (AFAB). This occurs in a ratio of 2:1 in AMABs to AFABs.

How will I know if I have renal oncocytoma?

Most often you will not have symptoms of renal oncocytima. If you do, the symptoms will be blood in the urine or pain with urination.¹ This is also rare, unlike kidney cancers.

What causes renal oncocytoma?

A definitive cause hasis not yet been identified. But if there are multiple renal oncocytomas, a syndrome called Birt Hogg Dube is suspected which is known to cause renal oncocytoma and another kidney tumour called chromophobe carcinoma.

How will renal oncocytoma be diagnosed?

• Imaging

Usually a scan such as ultrasound scan is enough to visualize this tumour. It usually appears like a well defined lesion with a scar in the kidney though this may be seen in many other conditions too.³ Some studies mention the word ‘spoke and wheel’ appearance on the scans ⁴ but lately it is established that this appearance is not limited to renal oncocytomas.⁴

• Biopsy 

This means sampling of the kidney or a renal biopsy. This procedure is done by introducing a needle through the side of your back, through the skin to the kidney and sampling the tumour. 

This sample which is a thin strip of tissue is then processed and sampled and checked 

under the microscope for its appearance.

• Immuno histochemistry

This means a particular kind of staining that binds to particular tumour cells and light them up under the microscope to enable identification.

These tumours stand out for their red, brown or mahogany colour surface that is well circumscribed and separate from the rest of the kidney, usually without a capsule.

Sometimes they may show a central scar, which is another clue to this diagnosis.

What is the treatment for renal oncocytoma?

There are several possible treatment options for renal oncocytoma.

• Watchful waiting: Since oncocytoma are non cancerous they can be observed over time with serial scans without the need to remove surgically. But sometimes they can grow large and invade adjacent tissues like fat around the kidney.
• Surgical resection: This tumour can be removed by surgery entirely. This can be done by complete or partial resection of the kidney.² Since it is a well rounded mass, it is easy to remove completely. Removing by surgery when there is no spread to other tissues is curative. 

Can I prevent renal oncocytomas?

Since no definitive cause for renal oncocytoma has been identified, no preventive measures are recommended.⁵

However, it is always important to bring any kidney related symptoms like blood in the urine to medical attention early, to diagnose any renal tumour at early stages for a better outcome.^6,7

What is the syndrome associated with renal oncocytoma?

• Birt-hogg dube is a syndrome that has an association with renal oncocytoma.

People with this syndrome have an increased chance of getting renal oncocytomas, another type of renal cancer called chromophobe cancer and cysts in the lungs that cause sudden difficulty in breathing. Those with this syndrome are said to develop about an average of 5.3 renal tumours in their life, including renal oncocytomas and chromophobe carcinoma.

• Tuberous sclerosis³

This is another syndrome that is associated with renal oncocytomas and several skin manifestations

FAQs

If I have renal oncocytoma, will I pass it down to my children?

If you have any of the associated syndromes mentioned above like Birt Hogg dube or tuberous sclerosis, those syndromes have some chance of passing down to family members.

Can there be more than one renal oncocytoma at a time?

Yes, renal oncocytomas are known to occur in multiples in the kidney. Sometimes they can even appear on both kidneys.⁴

Can renal oncocytomas spread to other organs?

Generally they are reported to be limited to kidney but rare cases in which they have spread to liver and bone have been reported.² 

Are there any other tumours connected to renal oncocytoma?

Yes, there is a kidney cancer called chromophobe carcinoma which can occur as a hybrid with a renal oncocytoma. This occurs as part of a syndrome called ‘Birt-hogg-dube’.

Is there any genetic defect associated with renal oncocytoma?

Yes, there are few genetic defects that can occur in these. But this doesn't mean this tumour is passed down the families. One common genetic defect is the rearrangement of a gene called CCDN1.¹

What is the outcome for renal oncocytoma?

This is a non cancerous tumour and the outcome is generally good.

Summary

Renal oncocytoma is a non cancerous growth of the kidney that rarely causes symptoms. Sometimes this tumour can occur in multiples or with a cancer called chromophobe cancer as part of a syndrome. Renal oncocytomas can either be surgically removed or monitored over time. They are not known to spread to other organs usually and have good outcomes.