What Is Kidney (Renal) Cancer

Cancer is when cells in the body change and grow out of control. These cells can form lumps of tissue called tumors. Cancer that starts in kidney cells is called kidney or renal cancer.

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Understanding the kidneys

The kidneys are 2 bean-shaped organs. Each is about the size of a bar of soap. They sit in the body towards the middle to lower part of the back. There is 1 kidney on each side of the spine. The kidneys help filter waste and excess fluid from the blood. The liquid and waste is then sent as urine to the bladder through thin tubes called ureters. Urine then leaves the body through a tube called the urethra. The kidneys also help control blood pressure. And they help make sure there are enough red blood cells in the body.

When kidney cancer forms

A kidney is made up of many layers of cells. Kidney cancer can affect any 1 or all of these layers. The cancer can stop the kidneys from working normally. Kidney cancer may spread to other parts of the body. When cancer spreads, it’s called metastasis. The more cancer spreads (metastasizes), the harder it is to treat.

Renal cell carcinoma (RCC)

The main type of kidney cancer is called renal cell carcinoma (RCC). About 9 out of 10 kidney cancer tumors are this type. If you have this type of kidney cancer, you may have more than 1 tumor in 1 or both kidneys. These may be large by the time they are diagnosed. But most cases of kidney cancer are found before the cancer has spread to other organs.

There are different types of RCC. A health care provider called a pathologist identifies these types by looking at the cancer cells under a microscope. The types of RCC include:

• Clear cell. This is the most common type of RCC. The cancer cells look pale or clear.
  
• Papillary. This is the second most common type of RCC. This type of tumor has tiny fingerlike growths.
  
• Chromophobe. This is a rare form of RCC. The cells are larger than other types of RCC.
  
• Collecting duct. This is also a rare form of RCC. The cancer cells look like irregular tubes.
  
• Unclassified. This includes tumors that have cells from more than 1 type of cancer. It also includes tumors with cells that don’t fit into the other categories.
  

Other types of kidney cancer

Other less-common types of kidney cancers include:

• Transitional cell carcinoma. This is also known as urothelial carcinoma. It starts where the ureter and kidney meet. This area is called the renal pelvis. This type of kidney cancer can act and look like bladder cancer.
  
• Wilms’ tumor. This cancer most always occurs in children. It's very rare in adults.
  
• Renal sarcoma. This is a very rare type of kidney cancer. It begins in the blood vessels and connective tissue around the kidneys.
  

Kidney tumors that aren’t cancer

There are several types of kidney tumors that are not cancer (benign). These include renal cell adenoma, renal oncocytoma, and angiomyolipoma. These types of tumors may still affect kidney function and can cause pain and other symptoms. But the cells usually do not spread to other organs.

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