What is Kidney Cancer

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Kidney Cancer (renal cell carcinoma)

What is kidney cancer?

Kidney cancer is a disease that begins in the kidneys. It occurs when healthy cells in one or both kidneys grow out of control and form a lump (called a tumor). Renal cell carcinoma is the most common type of kidney cancer in adults.

How common is kidney cancer?

Each year an estimated 75,000 patients are found with a kidney tumor. Approximately 65,000 of these are ultimately found to be renal cell carcinoma (kidney cancer).

The most common type is clear cell carcinoma. Renal cell cancer is not one disease but rather a collection of 15-20 types of renal tumors that can arise from the kidney. Kidney cancer is among the 10 most common cancers in both men and women, and the risk for developing kidney cancer is higher in men than in women. More information about kidney cancer risk factors >

Understanding the kidney

The kidneys are 2 bean-shaped organs. Each is about the size of a bar of soap or your fist. They are located towards the middle to lower part of the back, with one kidney on each side of the spine. The kidneys’ main function is to filter blood and produce urine which eliminates both excess fluids, electrolytes, and acids/bases from the body. By working in harmony with the rest of the body, the kidney maintains a comfortable balance or steady internal state (homeostasis) for the entire body. While some patients may live comfortably with only one kidney, maintaining excellent kidney function helps prevent excess stress on the body. Sometimes in the kidney, tumors can arise from the tubules responsible for urine production leading to renal cell carcinoma (kidney cancer). 

What are the types of kidney cancer (renal cell carcinoma)?

Renal Cell Carcinoma (RCC) is the most common type of kidney cancer, accounting for approximately 85% of all malignant kidney tumors. In RCC, cancerous (malignant) cells develop in the lining of the kidney tubules and grow into a mass called a tumor. Like many other cancers, the growth begins small and grows larger over time. RCC typically grows as a single mass. However, there are cases where a kidney may contain more than one tumor, or tumors are found in both kidneys at the same time.

Sub-Types of Renal Cell Carcinoma (RCC)

There are over a dozen sub-types of renal cell carcinoma that are identified by examining the tumor under a microscope. The most common types are:

  • Clear Cell - approximately 75% of individual cells appear very pale or clear under the microscope.
  • Papillary – approximately 10% to 15% of people have this form. These cancers form little finger-like projections (called papillae). There are two types of papillary tumors.
  • Chromophobe – approximately 5% of cases. These cells are larger and have prominent cell borders and can appear pink or clear.
  • Clear cell papillary – approximately 2-4% of all cases. A new subtype with features of both papillary and clear subtypes. These are often less aggressive.
  • Collecting Duct – approximately 1% of all cases. Aggressive type arising from the collecting system that forms irregular tubules.
  • Medullary – approximately 1% of cases. A very aggressive type often occurring in young African Americans with sickle trait.
  • Unclassified – approximately 2-3% of tumors that do not fit into any other category.

Other Types of Cancerous Kidney Tumors (Non-Renal Cell)

Less common types of cancerous tumors in the kidney include:

  • Urothelial Carcinoma: arise from the renal pelvis and resemble bladder cancer cells. These are genetically similar to urothelial cancer of the bladder and have similar risk factors such as cigarette smoking and occupational exposures to certain cancer-causing chemicals.
  • Wilms Tumor: a rare pediatric malignancy in children 2-5.
  • Renal Sarcoma: a rare type of kidney cancer (< 1%) arising from the connective tissue.
  • Benign (Non-Cancerous) Kidney Tumors 

Some types of kidney tumors are benign meaning they do not have the ability to spread (metastasize). Often these are treated unnecessarily. The UCLA Kidney Cancer Program is committed to identification and observation of these tumors:

  • Renal Adenoma: small, slow growing, benign tumors < 1 cm.
  • Oncocytoma: a renal tumor that can grow large but not spread. It often resembles kidney cancer on a biopsy. The UCLA Kidney Cancer Program has molecular imaging modalities to identify these types of tumors non-invasively.
  • Angiomyolipoma: a benign tumor containing fat, vessels, and muscle. When large they can bleed so treatment is advised when >4 cm.