What is a Renal Mass and What is a Localized Renal Tumor?

Parts of the kidney
Parts of the kidney
Image © 2003 Fairman Studios, LLC.

The word renal means kidney. The words "tumor" and "mass" mean abnormal growths in the body. A renal mass, or tumor, is an abnormal growth in the kidney. Some renal masses are benign (not cancerous) and some are malignant (cancerous).

One in four renal masses are benign. Smaller masses are more likely to be benign. Larger masses are more likely to be cancerous. Some tumors can be slow to grow while some can be aggressive. Aggressive tumors form, grow and spread very quickly.

Most diagnosed kidney growths are small and localized masses. Localized means that the tumor has not spread out from where it first started. Around 40% of kidney cancers are localized renal masses. Masses may be solid or cystic (having fluid). Most cystic masses are benign. 

Where are the Kidneys and What are they for?

The kidneys are two bean-shaped organs near the middle of the back. There is one kidney below the rib cage on each side of the spine. Each kidney is about the size of a fist.Our kidneys' main job is to filter the blood. The kidneys remove water and waste from our blood in the form of urine. Urine then leaves our body by way of the bladder and the urethra. As a filter, the kidneys:

  • Detoxify (clean) our blood
  • Balance fluids
  • Maintain electrolyte levels (e.g., sodium, potassium, calcium, magnesium, acid)
  • Remove waste (as urine)

The kidneys also make hormones that help to:

  • Keep blood pressure stable
  • Make red blood cells
  • Make bones stay strong

What do we Know about Kidney Cancers?

Kidney and renal pelvis cancers are the 12th leading cause of cancer death in the U.S. Kidney cancer is 9th on the list of the 10 most common types of cancer. Almost all of the kidney cancers in the U.S. are renal cell carcinomas (RCC). These cancers form in the lining of the small tubes in the kidney.

Doctors are able to diagnose kidney cancer earlier because of better testing. Kidney cancer is more common in men than women. More men than women die from the disease. Kidney cancer is more common in African Americans, American Indians and Alaskan Native people. You can get kidney cancer at any age. But, it is more common in older people (those greater than 75 years old).

There will be more than 65,000 new cases of kidney cancer in the U.S. in 2018. Of those cases, nearly 15,000 people will likely die from the disease. The earlier the cancer is diagnosed-the better the chances of survival. The five-year survival rate for all kidney cancers is about 74%. If the cancer spreads over the body, then this rate falls to about 12%. The five-year survival for localized kidney and renal pelvis cancer is 92.5%.

Around the world, over 300,000 people get kidney cancer each year. Half of those people will die from the disease. But, less people are dying each year from the disease.

Types of Renal Tumors

Renal tumors are grouped by where they start growing and by their structure. The main classes of tumors are:

  • Renal Cell Carcinomas (RCC). These are the most common malignant kidney tumors. They are found in the lining of the small tubes in the kidney. RCC may form as a single tumor within a kidney. It can also form two or more tumors in one kidney. 
  • Benign renal tumors. There are about 9 different types of tumors in this class. Some can grow quite large. But most are non-cancerous and do not spread to other organs. 
  • Wilms tumor. Wilms tumors almost always are found in children and are rarely found in adults.