Description
Kidney cancer is a malignant tumor that arises from the kidney tissues. A malignant tumor is an abnormal growth that has the potential of fast growth, destruction of the organ from which it arose, and spread to other organs and body parts. Untreated malignant tumors of the kidney are life threatening, as they grow and spread.
The two main types of cancers of the kidney are: Renal Cell Carcinoma and Transitional Cell Carcinoma. Renal Cell Carcinomas are the most common type of kidney cancer and arise from the corticomedullary compartment of the kidney (as described in the previous section). Transitional Cell Carcinomas arise from the collecting system of the kidney (as described in the above section).
Types/Subtypes of Kidney Cancer/Renal Cell Carcinoma (RCC)
Clear Cell (conventional)
This is the most common type of kidney cancer and accounts for 66-75% of all diagnosed cases. Clear cell RCC is the cell type associated with the von Hippel Lindau (VHL) gene mutation in hereditary kidney cancer. Approximately 70% of non-hereditary cases of clear cell RCC also have the VHL mutation.
Papillary
This is the second most common form of kidney cancer, comprising approximately 15% of cases. Papillary RCC is divided into two subtypes based on cell appearance: Type I (5%) and Type II (10%). There is an increased incidence of papillary RCC in African Americans and an increased incidence of bilateral disease (involving both kidneys) associated with this subtype. There are also hereditary forms of both Type I and Type II papillary RCC.
Chromophobe
This is a rare form of kidney cancer that represents approximately 5% of RCC diagnoses. This type of RCC is thought to originate from the same cell type as those that form renal oncocytomas. There is a familial or inherited form of chromophobe RCC (in association with renal oncocytoma) called Birt Hogg Dubé syndrome, which is also associated with a specific genetic mutation.
Renal Oncocytoma
This is a benign tumor of the kidney that comprises approximately 5% of all kidney tumors. These tumors do not metastasize, although they can grow to a large size in the kidney and invade local structures, which can result in symptoms requiring surgery. They are thought to be related to chromophobe RCC.
Unclassified
Less than 1% of renal cell carcinomas are an unclassified type and very rare. They don't fit into one of the more common subtypes of RCC listed above. When examined under a microscope, these unclassified cancer cells have a structure and genetic features that don't match the description of the more common RCC subtypes
Collecting Duct Carcinoma
This is a rare and very aggressive variant of kidney cancer that comprises less than 1% of cases. This form of RCC is usually metastatic (has spread to other organs) at the time of diagnosis, and is more common in younger individuals.
Medullary
This very rare and very aggressive variant of kidney cancer is thought to be a variant of collecting duct carcinoma. It is commonly associated with the sickle cell trait, and therefore is more common in the African-American population. It represents less than one percent of all kidney cancers diagnosed.
Sarcomatoid
This condition, known as "differentiation," can occur with any of the common RCC subtypes. The term refers to the fact that the RCC cells -- when viewed under the microscope -- have the appearance of sarcoma cells. The percentage of sarcomatoid differentiation is usually reflected in the tumor's pathology report and relates to the tumor's aggressiveness. The condition is found frequently in patients whose kidney cancer has metastasized widely.
Transitional Cell Carcinoma of the Kidney
Transitional cell carcinoma (TCC) of the kidney is a rare and potentially very aggressive tumor that should not be considered a true kidney cancer, but instead should be grouped with those cancers that develop from cells that line the urinary tract. This includes TCC of the urinary bladder, which is far more common than TCC of the kidney.
