Kidney cancer affects approximately 50,000 people in the United States each year. It occurs more often in men than in women. There are two main types of primary kidney tumors -- renal cortical tumors and transitional cell tumors. Of these, renal cortical tumors are far more common.
The Kidneys
The kidneys are two bean-shaped organs located deep inside the torso to the left and right of the backbone, in the area around the waist. Each kidney is about the size of an open hand and works independently to filter impurities and excess salts such as potassium and sodium from the blood. The kidneys process these wastes to form urine. Urine is concentrated and collected into a central funnel-like reservoir within the kidneys called the renal pelvis, also known as the collecting system. It is then passed down long, slender tubes that are about the diameter of pencils, called ureters, which connect the kidneys to the bladder.
Types of Kidney Cancer
Each kidney contains more than a million microscopic blood-processing filtering units called nephrons. Each nephron is associated with a microscopic renal tubule, which joins several other tubules from other nephrons to form collecting ducts. These ducts deposit the urine into the renal pelvis. When cancer arises in the area of the renal tubules, it is called a renal cortical tumor. Cancer that arises in the renal pelvis is called a transitional cell tumor.
About 90 percent of all kidney tumors are classified as renal cortical tumors. This term actually refers to a diverse group of tumor types that can exhibit very different clinical behaviors, meaning that the risk of spreading to other areas of the body varies. These tumors can be either benign or malignant (cancerous). Renal cortical tumors can be categorized into the following types:
- conventional, or clear cell, which accounts for 70 to 85 percent of cases
- papillary, also known as chromophil, which makes up 10 to 15 percent
- chromophobe, which accounts for 5 percent
- collecting duct, which makes up less than 1 percent
- unclassified, which makes up 3 to 5 percent
Tumors called oncocytomas are considered virtually benign lesions with almost no risk of spreading or causing death.
Papillary carcinomas can develop as individual tumors or as multiple tumors, appearing either in the same kidney or in both kidneys. There are two types of papillary cancers, type 1 and type 2. Type 1 papillary tumors are more common and usually grow slowly. Type 2 papillary tumors are much more aggressive tumors and may follow an unpredictable pattern of growth. Papillary carcinomas have been associated with a genetically inherited syndrome called hereditary leiomyomatosis and renal cell carcinoma (HLRCC). HLRCC is relatively rare and difficult to diagnose before surgery unless enough symptoms are present.
Chromophobe kidney tumors are also considered a less aggressive form of primary kidney cancer. These tumors may reach a very large size before there is any risk of them spreading outside the kidney.
Transitional cell tumors of the kidneys and ureters are similar to bladder tumors. The type of cells that line the inside of the bladder also line the inside of the ureters and the renal pelvis. Cancers that arise from these cells behave similarly, whether they grow in the bladder or in the collecting system (renal pelvis and ureter). Management of these lesions is completely different from that of renal cortical tumors and depends upon several factors including tumor grade, location, and size.
Low-grade transitional cell tumors that can be reached with a thin fiber-optic scope can sometimes be successfully treated using laser energy or electrocautery. High-grade tumors represent a much greater risk and more aggressive forms of treatment are typically recommended. Such treatment may include removal of the entire kidney and attached ureter leading down to the bladder. With both low- and high-grade tumors, initial diagnosis will depend on both the results of imaging studies and microscopic analysis of a tissue sample. The means by which the tumor sample is obtained will depend on the clinical situation. For more information about transitional cell tumors, visit the bladder cancer section on our Web site.
Not all masses found in the kidneys are renal cancers. Other types of masses include benign conditions such as angiomyolipomas (AML) and renal cysts. Both renal cysts and AML lesions have identifiable characteristics that can be seen on imaging studies and usually do not require treatment.
Certain types of cancers from other parts of the body, such as breast, lung, and skin cancers, can spread to the kidneys. Lymphoma can also be found in the kidney. How these diseases are evaluated and treated will depend on what other findings are present, including the extent of the original cancer.
