To understand more about kidney cancer, it helps to know about the normal structure and function of the kidneys.
The kidneys are a pair of bean-shaped organs, each about the size of a fist and weighing about 4 to 5 ounces. They are fixed to the upper back wall of the abdominal cavity, one on either side of the spine. Both are protected by the lower ribcage.
The kidneys' main job is to filter the blood to remove excess water, salt, and waste products. These substances become urine. Urine travels from the kidneys to the bladder through long slender tubes called ureters. The place where the ureter meets the kidney is called the renal pelvis. The urine is stored in the bladder until you urinate (pee).
The kidneys also help make sure the body has enough red blood cells. They do this by making a hormone called erythropoietin, which tells the bone marrow to make more red blood cells.
Our kidneys are important, but we actually need less than one complete kidney to function. Many people in the United States are living normal healthy lives with just one kidney. Some people may not have any working kidneys at all, and survive with the help of a medical procedure called dialysis. The most common form of dialysis uses a specially designed machine that filters blood much like a real kidney would.
Renal cell carcinoma (RCC), also known as renal cell cancer or renal cell adenocarcinoma, is by far the most common type of kidney cancer. About 9 out of 10 kidney cancers are renal cell carcinomas.
Although RCC usually grows as a single mass (tumor) within a kidney, sometimes there are 2 or more tumors in one kidney or even tumors in both kidneys at the same time. Some of these cancers are noticed only after they have become quite large, but most are found before they metastasize (spread) to distant organs in the body. Often they are found on CT scans or ultrasounds that are being done for concerns other than kidney cancer. Like most cancers, RCC is hard to treat once it has spread.
There are several subtypes of RCC, based mainly on how the cancer cells look under a microscope. Knowing an RCC subtype can be a factor in deciding treatment and can also help your doctor determine if your cancer may be due to an inherited genetic syndrome.
This is the most common form of renal cell carcinoma. About 7 out of 10 people with renal cell carcinoma have this kind of cancer. When seen under a microscope, the cells that make up clear cell RCC look very pale or clear.
This is the second most common subtype - about 1 case in 10 is this type. These cancers form little finger-like projections (called papillae) in some, if not most, of the tumor. Some doctors call these cancers chromophilic because the cells take in certain dyes and look pink under the microscope.
This subtype accounts for about 5% (5 cases in 100) of RCCs. The cells of these cancers are also pale, like the clear cells, but are much larger and have certain other features that can be recognized.
This subtype is very rare. The major feature is that the cancer cells can form irregular tubes.
Rarely, renal cell cancers are labeled as unclassified because the way they look doesn't fit into any of the other categories or because there is more than one type of cell present.
Other types of kidney cancers include transitional cell carcinomas, Wilms tumors, and renal sarcomas.
Of every 100 cancers in the kidney, about 5 to 10 are transitional cell carcinomas, also known as urothelial carcinomas. Transitional cell carcinomas don't start in the kidney itself, but instead begin in the lining of the renal pelvis (where the urine goes before it enters the ureter). This lining is made up of cells called transitional cells that look like the cells that line the bladder. When cancer develops from these cells they look like other urothelial carcinomas, such as bladder cancer, under the microscope. Studies have shown that, like bladder cancer, these cancers are often linked to cigarette smoking and being exposed to certain cancer-causing chemicals in the workplace.
People with transitional cell carcinoma often have the same signs and symptoms as patients with renal cell cancer − blood in the urine and, sometimes, back pain.
These cancers are usually treated by surgically removing the whole kidney and the ureter, as well as the portion of the bladder where the ureter attaches. Smaller, less aggressive cancers can sometimes be treated with less surgery. Chemotherapy (chemo) is sometimes given after surgery, depending on how much cancer is found. The chemo given is the same as that used for bladder cancer. It's important to talk with your doctor to be aware of your options and the benefits and risks of each treatment.
About 9 out of 10 transitional cell carcinomas of the kidney are curable if they are found at an early stage. The chances for cure drop dramatically if the tumor has grown into the ureter wall or main part of the kidney or if it has a more aggressive (high grade) appearance when seen under a microscope.
After treatment, follow-up visits to your doctor for monitoring with cystoscopy (looking into the bladder with a lighted tube) and imaging tests are extremely important because transitional cell carcinoma can come back in the bladder, as well as other places in the body.
Nephroblastomas, more commonly called Wilms tumors, almost always occur in children. This type of cancer is very rare among adults.
Renal sarcomas area rare type of kidney cancer (less than 1% of all kidney tumors) that begin in the blood vessels or connective tissue of the kidney.
Some kidney tumors are benign (non-cancerous). This means they do not metastasize (spread) to other parts of the body, although they can still grow and cause problems. Benign kidney tumors include renal cell adenomas, renal oncocytomas, and angiomyolipomas. They can be treated by removing or destroying the tumor, using many of the procedures that are also used for kidney cancers, such as radical nephrectomy, partial nephrectomy, radiofrequency ablation, and arterial embolization. The choice of treatment is influenced by many factors, such as the size of the tumor and if it is causing any symptoms, the number of tumors, whether tumors are present in both kidneys, and the patient’s general health.
Renal adenomas are the most common benign kidney tumors. They are small, slow-growing tumors that often show up on imaging tests (such as CT scans) when the doctor is looking for something else. Seen with a microscope, they look a lot like low-grade renal cell carcinomas. In rare cases, tumors first thought to be renal adenomas may turn out to be small renal cell carcinomas. Because they are hard to tell apart, suspected adenomas are often treated like renal cell cancers.
Oncocytomas are benign kidney tumors that can sometimes grow quite large. As with renal adenomas, it can sometimes be hard to tell them apart from kidney cancers. Because oncocytomas do not normally spread to other organs, surgery often cures them.
Angiomyolipomas are another rare benign kidney tumor. They often develop in people with tuberous sclerosis, a genetic condition that also affects the heart, eyes, brain, lungs, and skin. These tumors are made up of different types of connective tissues (blood vessels, smooth muscles, and fat). If they aren't causing any symptoms, they can often just be watched closely. If they start causing problems (like pain or bleeding), they may need to be treated.
The rest of this document focuses on renal cell carcinoma and not transitional cell carcinomas, Wilms tumors, renal sarcomas, or other less common types of kidney tumors.
Referenced from American Cancer Society (cancer.org)