The kidneys are two organs that filter waste products from the blood and form urine, as well as secrete vital hormones for proper body functioning. Kidney cancer, also referred to as renal cancer, occurs when cancer develops in normal kidney tissue.

To better understand kidney cancer, let’s take a quick look at how the kidneys function. Our kidneys—each the size of a fist—are a pair of bean-shaped organs that are attached to the upper back part of the abdominal wall—one on either side of the spine. Above each kidney sit the adrenal glands. The main job of the kidneys is to filter the blood coming in via the renal arteries to remove excess water, salt, and waste products—which collectively become urine. Urine leaves the kidneys via long slender tubes called ureters, which connect to the bladder. Urine is stored in the bladder until you urinate (or, more colloquially, pee). The place where the ureters meet the kidneys is called the renal pelvis. The kidneys also perform several other functions—they help:

• Control blood pressure by making a hormone called renin
• Make sure the body has enough red blood cells by making a hormone

While our kidneys are important, it’s interesting to note that we actually need less than one complete kidney to function. Many people are living normal, healthy lives with just one kidney. Some people, however, do not have any working kidneys, and they survive with the help of dialysis, a medical procedure that uses a special machine to filer the blood much the way a real kidney would. More than 1 million cases of cancer will be diagnosed this year. Kidney cancers only comprise 3% of these new cancers. Although nearly 13,000 people died from kidney cancer in the US in 2005, it is estimated that there are more than 100,000 kidney cancer survivors living in the US currently.

According to the National Cancer Institute, there are three main forms of renal cancer:

Renal cell cancer (RCC). RCC is the most common type of renal cancer in adults—accounting for 9 out of 10 kidney cancers—and stems from the cells that comprise the kidneys themselves.  It is now understood that many subtypes of RCC exist. For example, there are the following subtypes:

• Clear cell RCC (the most common type)—About 7 out of 10 people with RCC have this type of cancer. When seen under a microscope, the cells that make up clear cell RCC appear very pale or clear
• Papillary RCC—About 1 in 10 RCCs are of this type, making it the second most common subtype
• Chromophobe RCC—Accounts for about 5% of RCCs
• Rare types of RCC include:
  • Collecting duct RCC
  • Multilocular cystic RCC
  • Medullary RCC
  • Sarcomatoid RCC
  • Mucinous tubular and spindle cell carcinoma
  • Neuroblastoma-associated RCC
  • Unclassified RCC

Wilms tumor. Wilms tumors—or nephroblastomas—are the most common type of kidney cancer found in children, and are rarely found in adults.

Transitional cell cancer. Transitional cell cancer forms from tissues comprising the renal pelvis, or part of the urine collection system of the kidney, and the ureter, which carries urine from the kidneys to the bladder. Of every 100 cancers in the kidney, about 5 to 10 are transitional cell carcinomas (TCCs), also known as urothelial carcinomas. Transitional cell carcinoma is a more rare, but potentially very aggressive type of kidney or renal cancer. About 9 out of 10 TCCs of the kidney are cured if they are found at an early stage. The chances for cure are lower if the tumor has grown into the ureter wall or main part of the kidney or if it looks more aggressive (high grade) when seen under a microscope.

Benign (non-cancerous) kidney tumors

There are also a number of benign—non-cancerous—kidney tumors, which means that they do not metastasize or spread throughout the body, but can nonetheless still grow and cause considerable trouble. Benign kidney tumors can be treated by either removing or destroying them, using many of the same treatments utilized for kidney cancers, like surgery, radiofrequency ablation, and arterial embolization. Choice of treatment  hinges on many factors, like the size of the tumor and if it is causing any symptoms, number of tumors, whether tumors are in one or both kidneys, and the person’s overall health. These are the main types of benign kidney tumors:

• Renal adenoma. These are the most common benign kidney tumors; which often look a lot like low-grade renal cell carcinomas.
• Oncocytoma. These benign kidney tumors sometimes grow quite large.  Similar to renal adenomas, they can sometimes be hard to tell apart from kidney cancers.
• Angiomyolipoma. Angiomyolipomas are rare. They often develop in people with tuberous sclerosis, a genetic condition that also affects the heart, eyes, brain, lungs, and skin.