Kidney cancer, like other cancer, starts when the normal cells in one or both kidneys change and grow uncontrollably. These form a mass or a tumor. A tumor can be benign or non-cancerous or may be malignant or cancerous. A cancerous tumor has the ability to spread to other parts of the body.
There are several types of kidney cancer. Some of these include:
Renal cell carcinoma
This is the most common type of kidney cancer and accounts for 80 to 85% of all cases. This cancer develops within the kidney's microscopic filtering systems. These are tiny tubes that carry the urine to formation. These tubules of tiny tubes join to form a network of tubes and form progressively larger tubes that lead to formation of the ureter that drains the urine into the bladder.
Transitional cell carcinoma
This is also called the urothelial carcinoma. This starts usually in the area of the kidney where urine collects before moving to the bladder. This cancer is pathologically (in cellular appearance) similar to bladder cancer and is treated like bladder cancer. It accounts for 10% to 15% of kidney cancer in adults.
Kidney sarcoma
This is a rare form of kidney cancer and is usually treated with surgery and chemotherapy. Sarcomas may grow large in size and usually does not spread as commonly as other types of kidney cancer.
Wilms tumor
This is a common type of kidney cancer seen among children and is treated differently than kidney cancers in adults. Treatment involves radiation therapy and chemotherapy more commonly.
Other types
These include Squamous cell carcinoma, Juxtaglomerular cell tumor (also called reninoma), Bellini duct carcinoma, Mesoblastic nephroma, Mixed epithelial stromal tumors etc.
Kidney cancers that have begun elsewhere include Clear cell adenocarcinoma, Transitional cell carcinoma (from bladder), inverted papilloma, Renal lymphoma, Teratoma, carcinosarcoma and carcinoid tumor of the renal pelvis. Cancer may also be the result of metastasis from other organs.
Different types of kidney cancer cells
Different types of kidney cancer affect different types of cells within the kidney. These are seen by the pathologist under the microscope and the cellular diversity helps plan treatment pattern for different types of kidney cancers. There are nearly 10 different types of kidney cancer cells. These include:
Clear cell
This is the commonest type of cell found in about 70% of kidney cancers. These may be slow growing or grade 1 with less aggressive nature or may be fast growing or grade 4 with a more aggressively growing nature. Clear cells are susceptible to treatment with immunotherapy and targeted therapy.
Papillary cancer cells
This type of kidney cancer is seen in 10% to 15% of patients and has further subtypes called type 1 and type 2. They are different from the clear cell type but are treated similarly.
Sarcomatoid cells
These grow the fastest of all types of kidney cancer cells. It may be found with clear cell or papillary type. The cancer cells appear like sarcoma cells under the microscope.
Collecting duct cancer
This is similar to transitional cell carcinoma and is rare. It is treated with chemotherapy.
Oncocytoma
This is a slow growing cancer and does not spread beyond the kidneys. Chromophobe is another rare cancer. Angiomyolipoma is a non- cancerous tumor that has a unique appearance on the computed tomography (CT or CAT) scan. This type of cancer is less likely to grow aggressively and spread. It is treated with surgery.
Further Reading