The kidney is made up of many layers of cells. Kidney cancer can affect any one or all of these layers.
Renal Cell Carcinoma
The main type of kidney cancer is called renal cell carcinoma. It begins in a layer of tissue called the renal tubular epithelium. More than 9 out of 10 malignant kidney tumors are this type. If you have this type of kidney cancer, you may have more than one tumor in one or both kidneys. These may be quite large by the time they are diagnosed. But most are found before they have spread, called metastasized, to other organs. If you have renal cell carcinoma, you will have one of 5 types. The pathologist identifies these types by looking at the cancer cells under a microscope. There appears to be a link between the type of renal cell carcinoma and how it behaves.
Clear cell. About 80 percent of people with renal cell carcinoma have this type, making it the most common type. It appears pale or clear under the microscope.
Papillary. This is the second most common type of renal cancers, accounting for 10 to 15 percent of cases. These look pink from preparation of the tissue before examination. These cancers also form tiny fingerlike projections, which gives them a tubular appearance.
Chromophobe. This is a rare form of kidney cancer, making up about 5 percent of cases. Pale in color, these cells are larger than other types of renal cell carcinoma.
Collecting duct. These are very rare. These cancer cells form irregular tubes.
Unclassified. This includes kidney cancer cells from multiple types or cells that do not fit into the other categories.
In some cases, the term sarcomatoid may be used to describe kidney cancer. This adjective can be used to describe any of the types of kidney cancer listed above. Some experts believe that sarcomatoid kidney cancers are more difficult to treat.
Most of the treatments for kidney cancer have been developed for clear cell tumors. Data regarding how well a particular treatment works for kidney cancer generally does not apply to the other subtypes.
Other Types of Kidney Cancer
There are other less common types of kidney tumors. These types are not covered in this section.
Transitional cell carcinoma. These account for about 5 percent to 10 percent of all kidney tumors. They are also known as urothelial carcinomas. They begin in the junction between the ureter and kidney, which is called the renal pelvis. They can act and look very much like bladder cancer.
Wilms’ tumor. This cancer is almost always found in children. It accounts for 5 to 6 percent of all kidney cancers.
Renal sarcoma. This is a very rare type of kidney cancer. It begins in the kidney’s connective tissue.
Non-cancerous Kidney Tumors
There are also several types of benign (non-cancerous) kidney tumors including renal cell adenomas, renal oncocytomas, and angiomyolipomas.