The kidneys

Most people have two kidneys. They sit at the back of the body, one on each side, just underneath the ribcage. They filter the blood to remove waste products, which they convert into urine. Urine is carried from each kidney, through a tube called a ureter to the bladder, where it is stored.

When you are ready to pass urine, it leaves the bladder through a tube called the urethra. The urethra opens immediately in front of the vagina in women and at the tip of the penis in men.

Diagram showing the structure of the kidneys

What is cancer?

The organs and tissues of the body are made up of tiny building blocks called cells. Cancer is a disease of these cells.

Cells in different parts of the body may look and work differently but most reproduce themselves in the same way. Cells are constantly becoming old and dying, and new cells are produced to replace them. Normally, cells divide in an orderly and controlled manner. If for some reason the process gets out of control, the cells carry on dividing, developing into a lump which is called a tumour.

Tumours can be either benign or malignant. Cancer is the name given to a malignant tumour. Doctors can tell if a tumour is benign or malignant by examining a small sample of cells under a microscope. This is called a biopsy.

In a benign tumour the cells do not spread to other parts of the body and so are not cancerous. However, if they continue to grow at the original site, they may cause a problem by pressing on the surrounding organs.

A malignant tumour consists of cancer cells that have the ability to spread beyond the original area. If the tumour is left untreated, it may spread into and destroy surrounding tissue. Sometimes cells break away from the original (primary) cancer. They may spread to other organs in the body through the bloodstream or lymphatic system.

The lymphatic system is part of the immune system - the body's natural defence against infection and disease. It is a complex system made up of organs, such as bone marrow, the thymus, the spleen, and lymph nodes. The lymph nodes (or glands) throughout the body are connected by a network of tiny lymphatic ducts.

When the cancer cells reach a new area they may go on dividing and form a new tumour. This is known as a secondary cancer or metastasis.

It is important to realise that cancer is not a single disease with a single type of treatment. There are more than 200 different kinds of cancer, each with its own name and treatment.

Types of cancer

Carcinomas

The majority of cancers, about 85% (85 in a 100), are carcinomas. They start in the epithelium, which is the covering (or lining) of organs and of the body (the skin). The common forms of breast, lung, prostate and bowel cancer are all carcinomas.

Carcinomas are named after the type of epithelial cell that they started in and the part of the body that is affected. There are four different types of epithelial cells:

• squamous cells - that line different parts of the body, such as the mouth, gullet (oesophagus), and the airways
• adeno cells - form the lining of all the glands in the body and can be found in organs such as the stomach, ovaries, kidneys and prostate
• transitional cells - are only found in the lining of the bladder and parts of the urinary system
• basal cells - that are found in one of the layers of the skin.

A cancer that starts in squamous cells is called a squamous cell carcinoma. A cancer that starts in glandular cells is called an adenocarcinoma. Cancers that start in transitional cells are transitional cell carcinomas, and those that start in basal cells are basal cell carcinomas.

Leukaemias and lymphomas

These occur in the tissues where white blood cells (which fight infection in the body) are formed, i.e. the bone marrow and lymphatic system. Leukaemia and lymphoma are quite rare and make up about 6.5% (6.5 in 100) of all cancers.

Sarcomas

Sarcomas are very rare. They are a group of cancers that form in the connective or supportive tissues of the body such as muscle, bone and fatty tissue. They account for less than 1% (1 in 100) of cancers.

Sarcomas are split into two main types:

• bone sarcomas - that are found in the bones
• soft tissue sarcomas - that develop in the other supportive tissues of the body.

Others forms of cancer

Brain tumours and other very rare forms of cancer make up the remainder of cancers.

Types of kidney cancer

Each year, about 6200 people in the UK are diagnosed with kidney cancer. It affects more men than women and becomes more common as people get older. It is rare for people under 40 to get kidney cancer, but there is an uncommon type (Wilms' tumour, also known as nephroblastoma) that affects very young children.

Cancer of the kidney isn't infectious and can't be passed on to other people. Usually only one kidney is affected.

It is rare for cancer to occur in the other kidney.

About 90% of kidney cancers are renal cell cancers (RCC). They are sometimes called renal adenocarcinoma. There are different subtypes of renal cell cancer which can be identified by looking at the cells under a microscope. The most common subtype is clear cell. Other, less common, types include papillary (or chromophilic), chromophobic, oncocytic, collecting duct and sarcomatoid.

There is a rarer type of kidney cancer, known as transitional cell cancer (TCC), which starts in the cells lining the central area of the kidney (the renal pelvis). The tests and treatment for transitional cell cancer are very different.

This booklet describes the tests and treatments for renal cell cancers. Our factsheet on cancer of the ureter and renal pelvis covers the treatment of transitional cell cancer.

Causes of kidney cancer

Doctors don't know exactly what causes kidney cancer and for many people the cause is never found, but a number of things are known to increase the risk of developing it.

Cigarette smoking This may increase the risk by as much as double for some people. The longer a person smokes for and the more cigarettes they smoke, the greater the risk.

Being overweight (obese) People who weigh at least a quarter (25%) more than is recommended for their height have a higher than average risk of getting kidney cancer.

Some medical conditions, such as having high blood pressure (hypertension) may increase the risk. People with advanced kidney disease, especially those who need to have dialysis, have a higher risk of developing kidney cancer.

Exposure to certain materials at work may affect a person's risk. Working with blast furnaces or coke-ovens, in the steel and coal industries has been linked to an increased risk of kidney cancer. Being exposed to cadmium, lead or asbestos at work may also increase risk.

Most kidney cancers aren't inherited but occasionally, two or more members of the same family develop kidney cancer. If this happens, other members of the family may have a higher than average risk of getting kidney cancer.

There are some rare conditions, such as von Hippel-Lindau disease, where an inherited faulty gene increases the risk of developing kidney cancer. Kidney cancers that develop because of inherited faulty genes have some differences from other kidney cancers. They are more likely to cause several tumours and to affect both kidneys. They are also more likely to happen at a younger age than other kidney cancers.