What are the kidneys?

The kidneys are bean-shaped organs located below the ribcage near the middle of your back. Most people have two kidneys, each about the size of a fist, one on each side of the spine.

What do the kidneys do?

The kidneys have four main functions in the body:

  • To maintain fluid balance.
  • To remove waste products.
  • To control blood pressure.
  • To produce hormones needed to make blood and to maintain strong bones (Hormones are chemical messengers that stimulate or control the activity of cells or organs.).

Blood passes through the kidneys to be cleaned before returning to the heart. Blood enters the kidneys through two vessels called renal arteries. Within the kidney are millions of tiny structures called nephrons. The nephrons are the actual filters that remove the waste products and fluid from the blood.

The kidneys also produce urine, which is made up of excess water and waste products filtered from the blood. The urine travels to the bladder (a balloon-shaped storage pouch) through two tubes called ureters. The bladder empties urine from the body (urination) through another tube called the urethra.

The kidneys regulate blood pressure by controlling how much water is in the blood (blood volume). More blood volume means the heart has more fluid to pump and there is more force against the walls of the blood vessels, which results in higher blood pressure. The kidneys control blood volume by secreting a special hormone and by changing the balance of certain chemicals in the blood. These chemicals include potassium and sodium.

The kidneys also produce several important hormones, including:

  • Erythropoietin: This hormone triggers the bone marrow (the soft, spongy tissue inside the large bones of the body where blood cells are formed) to make red blood cells. Red blood cells carry oxygen to the body's cells.
  • Renin: This hormone regulates blood pressure.
  • Calcitriol: This hormone tells the intestines to absorb calcium from the foods we eat. Calcium is a mineral that helps maintain healthy bones and teeth.

What is kidney cancer?

Kidney cancer is the abnormal growth of cells in kidney tissue. In time, these cells form a mass called a tumor. Cancer begins when something triggers a change in the cells, and they divide out of control. A cancerous or malignant tumor can spread (metastasize) to other tissues and vital organs.

What are the types of kidney cancer?

The information in this document refers to renal cell carcinoma – the most common form of kidney cancer. However, there are different types of kidney cancer, including:

  • Renal cell carcinoma (RCC): This is the most common form of kidney cancer in adults and accounts for 85% of all kidney cancers. Renal cell carcinoma usually develops as a single tumor in one kidney, but it can affect both kidneys. Renal cell carcinoma begins in the cells that line the small tubes that are part of the nephrons within the kidneys. (Renal is the Latin word for kidney, and the term "carcinoma" refers to cancer that begins in the cells that line or cover an organ.).
  • Transitional cell carcinoma: Transitional cell carcinoma accounts for 6% to 7% of all kidney cancers. This cancer usually begins in the area where the ureter connects to the main part of the kidney. This area is called the renal pelvis. Transitional cell carcinoma also can occur in the ureters or bladder.
  • Renal sarcoma: This is the least common form of kidney cancer, accounting for only 1% of kidney cancer cases. It begins in the connective tissues of the kidneys and, if not treated, can spread to nearby organs and bones.
  • Wilms' tumor: This is the most common type of kidney cancer in children. It accounts for about 5% of kidney cancers.

How common is kidney cancer?

Kidney cancer represents about 3.7 percent of all cancers in the United States. Each year, more than 62,000 Americans are diagnosed with kidney cancer. The risk of kidney cancer increases with age. It is more common in men than in women.

Stages of kidney cancer

  • Stage I: The tumor is 7 cm across or smaller and is only in the kidney. It has not spread to lymph nodes or other tissue. (Lymph nodes are small "filters" that trap germs and cancer cells, and store infection-fighting cells.).
  • Stage II: The tumor is larger than 7 cm across but is still only in the kidney. It has not spread to lymph nodes or other tissue.
  • Stage III: The tumor has spread to the major blood vessels – the renal vein and inferior vena cava – or into the tissue surrounding the kidney, or to nearby lymph nodes.
  • Stage IV: The tumor has spread outside of the kidney to the adrenal gland (the small gland that sits on top of the kidney), or to distant lymph nodes, or to other organs.

Tumors are also graded, which is a way of rating a tumor based on how abnormal its cells look. Tumor grading can also tell the doctor how fast the tumor is likely to grow. Tumors whose cells do not look like normal cells and divide rapidly are called high-grade tumors. High-grade tumors tend to grow and spread more quickly than low-grade tumors.

What causes kidney cancer?

The exact cause of kidney cancer is not known, but several risk factors have been identified. A risk factor is a characteristic or behavior that increases your chance of developing a disease. Risk factors for kidney cancer include:

  • Smoking: Smokers are at greater risk for kidney cancer. In addition, the longer a person smokes, the higher the risk.
  • Obesity: Obesity is a risk factor for kidney cancer. In addition, the more overweight a person is, the higher the risk.
  • High blood pressure: Also called hypertension, high blood pressure has been linked to an increased risk of kidney cancer.
  • Family history: People who have family members with kidney cancer may have an increased risk of developing cancer themselves.
  • Radiation: Women who have been treated with radiation for cancer of the reproductive organs may have a slightly increased risk for developing kidney cancer.
  • Gene changes (mutations): Genes contain instructions for a cell's function. Changes in certain genes can increase the risk of developing kidney cancer.
  • Long-term dialysis treatment: Dialysis is the process of cleaning the blood by passing it through a special machine. Dialysis is used when a person's kidneys are not functioning properly.
  • Tuberous sclerosis: Tuberous sclerosis is a disease that causes seizures and mental retardation, as well as the formation of tumors in many different organs.
  • Von Hippel-Lindau (VHL) disease: People with this inherited disorder are at greater risk for developing kidney cancer. This disorder causes non-cancerous tumors in the blood vessels, typically in the eyes and brain.

What are the symptoms of kidney cancer?

Kidney cancer may not produce any noticeable symptoms in its early stages. However, as the tumor grows, symptoms may begin to appear. For that reason, kidney cancer is often not diagnosed until it has begun to spread.

Symptoms of kidney cancer can include:

  • Blood in the urine (a condition called hematuria).
  • A lump or mass in the kidney area.
  • Pain in the side.
  • Tiredness.
  • A general sense of not feeling well.
  • Loss of appetite and/or weight.
  • Low-grade fever.
  • Bone pain.
  • High blood pressure.
  • Anemia (a condition that results from not having enough red blood cells).

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