About the kidneys
Every person has 2 kidneys, which are located above the waist on both sides of the spine. These reddish-brown, bean-shaped organs are each about the size of a small fist. They are located closer to the back of the body than to the front.
The kidneys filter blood to remove impurities, excess minerals and salts, and extra water. Every day, the kidneys filter about 200 quarts of blood to generate 2 quarts of urine. The kidneys also produce hormones that help control blood pressure, red blood cell production, and other bodily functions.
Most people have 2 kidneys. Each kidney works independently. This means the body can function with less than 1 complete kidney. With dialysis, a mechanized filtering process, it is possible to live without functioning kidneys. Dialysis can be done through the blood, called hemodialysis, or by using the patient’s abdominal cavity, called peritoneal dialysis.
About kidney cancer
Kidney cancer begins when healthy cells in 1 or both kidneys change and grow out of control, forming a mass called a renal cortical tumor. A tumor can be malignant, indolent, or benign. A malignant tumor is cancerous, meaning it can grow and spread to other parts of the body. An indolent tumor is also cancerous, but this type of tumor rarely spreads to other parts of the body. A benign tumor means the tumor can grow but will not spread.
Types of kidney cancer
There are several types of kidney cancer:
- Renal cell carcinoma. Renal cell carcinoma is the most common type of adult kidney cancer, making up about 85% of diagnoses. This type of cancer develops in the proximal renal tubules that make up the kidney’s filtration system. There are thousands of these tiny filtration units in each kidney. The treatment options for renal cell carcinoma are discussed later in this guide.
- Urothelial carcinoma. This is also called transitional cell carcinoma. It accounts for 5% to 10% of the kidney cancers diagnosed in adults. Urothelial carcinoma begins in the area of the kidney where urine collects before moving to the bladder, called the renal pelvis. This type of kidney cancer is treated like bladder cancer because both types of cancer begin in the same cells that line the renal pelvis and bladder.
- Sarcoma. Sarcoma of the kidney is rare. This type of cancer develops in the soft tissue of the kidney; the thin layer of connective tissue surrounding the kidney, called the capsule; or surrounding fat. Sarcoma of the kidney is usually treated with surgery. However, sarcoma commonly comes back in the kidney area or spreads to other parts of the body. More surgery or chemotherapy may be recommended after the first surgery.
- Wilms tumor. Wilms tumor is most common in children and is treated differently from kidney cancer in adults. Wilms tumors make up about 1% of kidney cancers. This type of tumor is more likely to be successfully treated with radiation therapy and chemotherapy than the other types of kidney cancer when combined with surgery. This has resulted in a different approach to treatment.
- Lymphoma. Lymphoma can enlarge both kidneys and is associated with enlarged lymph nodes, called lymphadenopathy, in other parts of the body, including the neck, chest, and abdominal cavity. In rare cases, kidney lymphoma can appear as a lone tumor mass in the kidney and may include enlarged regional lymph nodes. If lymphoma is a possibility, your doctor may perform a biopsy (see Diagnosis) and recommend chemotherapy instead of surgery.
Types of kidney cancer cells
Knowing which type of cell makes up a kidney tumor helps doctors plan treatment. Pathologists have identified more than 40 different types of kidney cancer cells. A pathologist is a doctor who specializes in interpreting laboratory tests and evaluating cells, tissues, and organs to diagnose disease. Computed tomography (CT) scans or magnetic resonance imaging (MRI) (see Diagnosis) cannot always show the difference between benign, indolent, or malignant renal cortical tumors before surgery.
The most common types of kidney cancer cells are listed below. In general, the grade of a tumor refers to the degree of differentiation of the cells, not how fast they grow. Differentiation describes how much the cancer cells look like healthy cells. The higher the grade, the more likely the cells are to spread or metastasize over time.
- Clear cell. About 70% of kidney cancers are made up of clear cells. Clear cells range from slow growing (grade 1) to fast growing (grade 4). Immunotherapy and targeted therapy (see Types of Treatment) are particularly effective at treating clear cell kidney cancer.
- Papillary. Papillary kidney cancer is found in 10% to 15% of all kidney cancers. It is divided into 2 different subtypes, called type 1 and type 2. Localized papillary kidney cancer is often treated with surgery. If papillary kidney cancer spreads or metastasizes, it is often treated with blood vessel blocking agents. Using immunotherapy to treat metastatic papillary cancers is still being researched. Many doctors recommend treatment through a clinical trial for metastatic papillary cancers.
- Sarcomatoid features. Each of the tumor subtypes of kidney cancer (clear cell, chromophobe, and papillary, among others) can show highly disorganized features under the microscope. These are often described by pathologists as “sarcomatoid.” This is not a distinct tumor subtype, but when these features are seen, doctors are aware that this is a very aggressive form of kidney cancer. There is promising scientific research for immunotherapy treatment options for people with a tumor with sarcomatoid features. Most recently, this included the approved combinations of ipilimumab (Yervoy) and nivolumab (Opdivo), axitinib (Inlyta) and pembrolizumab (Keytruda), axitinib and avelumab (Bavencio), cabozantinib (Cabometyx) and nivolumab, and lenvatinib (Lenvima) and pembrolizumab, as well as the experimental combination of atezolizumab (Tecentriq) and bevacizumab (Avastin).
- Medullary. This is a rare and highly aggressive cancer but is still considered a renal cortical tumor. It is more common in Black people and is highly associated with having sickle cell disease or sickle cell trait. Sickle cell trait means that a person has inherited 1 copy of the sickle cell gene from a parent. Combinations of chemotherapy are currently recommended treatment options, and clinical trials are ongoing to better define treatment decisions.
- Collecting duct: Collecting duct carcinoma is more likely to occur in people between the ages of 20 and 30. It begins in the collecting ducts of the kidney. Therefore, collecting duct carcinoma is closely related to transitional cell carcinoma (see “Urothelial carcinoma,” above). This is cancer is difficult to treat successfully long term, even with combinations of systemic chemotherapy and surgery.
- Chromophobe. Chromophobe is another uncommon cancer that may form indolent tumors that are unlikely to spread but are aggressive if they do spread. Clinical trials are ongoing to find the best ways to treat this type of cancer.
- Oncocytoma. This is a slow-growing type of kidney cancer that rarely, if ever, spreads. The treatment of choice is surgery for large, bulky tumors.
- Angiomyolipoma. Angiomyolipoma is a benign kidney tumor that has a unique appearance on a CT scan and when viewed under a microscope. Usually, it is less likely to grow and spread. It is usually treated with surgery or, if it is small, with active surveillance (see Types of Treatment). Significant bleeding is a rare event but more likely when female patients are pregnant and before menopause. An aggressive form of angiomyolipoma, called epithelioid, can in rare instances invade the renal vein and inferior vena cava and spread to nearby lymph nodes or organs, such as the liver.