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What Are Kidney Tumors?

Kidney tumors, also called renal tumors, are growths in the kidneys that can be benign (noncancerous) or malignant (cancerous).

Types of Kidney Tumors

Benign kidney tumors can be treated by removing or destroying them, using many of the same treatments that are also used for malignant kidney tumors.  The choice of treatment depends on the size of the tumor and if it is causing any symptoms, the number of tumors, whether tumors are in both kidneys, and the person’s general health.

Types of benign kidney tumors include:

  • Renal adenoma – Renal adenomas are the most common form of benign, solid kidney tumor, and are typically small, low-grade growths. Their cause is unknown.
  • Renal oncocytoma – Oncocytoma is a benign, usually asymptomatic tumor that can grow quite large.  They can develop throughout the body and are not unique to the kidneys.  Their cause is also unknown, and they appear with greater frequency in men than in women.
  • Angiomyolipoma – Also known as renal hamartoma, angiomyolipomas are rare, benign tumors that can be caused by an inherited genetic mutation.  They can occur on an isolated, individual basis, but most often are associated with a rare genetic disease called tuberous sclerosis, which can cause tumors in the skin, kidneys, brain, and other organ systems.  In patients without tuberous sclerosis, these tumors most often occur in middle-aged women.
  • Fibroma – Fibromas are tumors of the fibrous tissue on, in, or surrounding the kidney. They are rare and more common in women.  Their cause is unknown and most do not cause symptoms.
  • Lipoma – Lipomas are rare renal tumors originating in the fat cells within the renal capsule or surrounding tissue. Lipomas typically occur in middle-aged women.

Renal cell carcinoma (RCC), also known as renal cell cancer or renal cell adenocarcinoma, is the most common type of malignant kidney tumor.  According to the American Cancer Society, about 9 out of 10 kidney cancers are renal cell carcinomas.

There are several subtypes of RCC, based mainly on how the cancer cells look in the lab. Knowing the subtype of RCC can be a factor in deciding treatment and can also help your doctor determine if your cancer might be caused by an inherited genetic syndrome.Subtypes of RCC include:

  • Clear cell renal cell carcinoma – This is the most common form of renal cell carcinoma.  About 7 out of 10 people with RCC have this kind of cancer. When seen under a microscope, the cells that make up clear cell RCC look very pale or clear.
  • Papillary renal cell carcinoma – This is the second most common subtype.  About 1 in 10 RCCs are of this type.  These cancers form little finger-like projections (called papillae) in some, if not most, of the tumor.  Some physicians call these cancers chromophilic because the cells take in certain dyes and look pink under the microscope.
  • Chromophobe renal cell carcinoma – This subtype accounts for about 5% (5 cases in 100) of RCCs.  The cells of these cancers are also pale, like the clear cells, but are much larger and have certain other features that can be recognized when looked at with a microscope.
  • Rare types of renal cell carcinoma – These subtypes are very rare, each making up less than 1% of RCCs:
    • Collecting duct RCC
    • Multilocular cystic RCC
    • Medullary carcinoma
    • Mucinous tubular and spindle cell carcinoma
    • Neuroblastoma-associated RCC
  • Unclassified renal cell carcinoma – Rarely, renal cell cancers are labeled as unclassified because the way they look doesn’t fit into any of the other categories or because there is more than one type of cell present.


Kidney cancer usually does not have symptoms in its early stages. In time, signs and symptoms may develop, including:

  • Blood in your urine
  • Pain or a lump in the lower back
  • Loss of appetite
  • Unexpected weight loss
  • Fever
  • Anemia
  • Fatigue

Because these symptoms may overlap with those of other conditions, it is important to get the correct diagnosis to find the right treatment. Make an appointment with your primary care physician if you are experiencing persistent signs and symptoms that concern you.

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