Cancer

Cancer begins with an alteration to the structure of the deoxyribonucleic acid (DNA) that is found in all human cells. This is known as a genetic mutation. The DNA provides the cells with a basic set of instructions, such as when to grow and reproduce.

The mutation in the DNA changes these instructions so that the cells carry on growing. This causes the cells to reproduce in an uncontrollable manner, producing a lump of tissue that is known as a tumour.

Most cancers grow and spread to other parts of the body through the lymphatic system. The lymphatic system is a series of glands (or nodes) that are spread throughout your body in a similar way to your blood circulation system. The lymph glands produce many of the specialised cells that are needed by your immune system.

Kidney cancer usually spreads into blood vessels that are located near to the kidney or the adrenal gland. The adrenal gland is an organ that releases adrenaline, which is a naturally produced hormone that the body uses during stressful situations.

The cancerous cells are spread through the lymphatic system into other organs of the body. The most common places for kidney cancer to spread are:

• the lungs
• muscles, ligaments and tendons
• bone
• liver
• skin
• central nervous system

Common risk factors

The three leading risk factors for kidney cancer are:

• smoking
• obesity
• high blood pressure (hypertension)

Each risk factor is discussed in more detail below.

Smoking

Smoking is a significant risk factor for developing kidney cancer, and the more you smoke the greater the risk.

For example, research has shown that if you regularly smoke 10 cigarettes a day, you are 150% more likely to develop kidney cancer compared to a non-smoker. This is increased to 200% if you smoke 20 or more cigarettes a day.

It is not clear why smoking increases your chances of developing kidney cancer.

Obesity

Obesity is another important risk factor for cancer of the kidney, particularly in women.

One way of assessing a person's weight is to measure their Body Mass Index (BMI). See the common health question called How can I work out my body mass index (BMI)? to work out what your BMI is. Alternatively, you can use the healthy weight calculator.

Research has found that there is a strong link between someone's BMI and their risk of developing kidney cancer.

Men who have a BMI score of between 25 and 29.9 are overweight and have an 18% increase in their risk of developing kidney cancer.

Women with a BMI score in this category have a 32% increase in their risk of developing kidney cancer

Men who have a BMI score of 30 or above are obese and have a 55% increase in their risk of developing kidney cancer. Women with a BMI score of 30 or above have an 85% increase in their risk of developing kidney cancer.

One theory as to why being overweight or obese increases a person's risk of developing kidney cancer is that overweight or obese people, particularly women, have higher levels of a hormone called oestrogen in their body. It is thought that excess levels of oestrogen may stimulate the growth of cancerous cells.

High blood pressure

People with poorly controlled high blood pressure who need medication to help lower it are up to twice as likely to develop kidney cancer compared with the population at large. This could be due to several reasons. For example:

• high blood pressure is associated with smoking and obesity, so these two factors could be increasing the risk
• high blood pressure can be caused by kidney disease, so there may be a kidney condition that has yet to be identified that causes both high blood pressure and kidney cancer

Possible risk factors

A number of other possible risk factors for kidney cancer include:

• exposure to certain chemicals such as asbestos and cadmium: asbestos is a mineral that was widely used in the construction industry but was banned in 1999, and cadmium is a metal used to manufacture batteries
• tuberous sclerosis: a rare genetic condition that causes multiple non-cancerous tumours to grow in the body -an estimated 1 in every 100 people with tuberous sclerosis will develop kidney cancer
• Von Hippel-Lindau disease: another rare genetic condition that causes small non-cancerous tumours to develop inside the nervous system - people with the condition have about a one in three chance of developing kidney cancer
• cocaine misuse: cocaine itself does not cause kidney cancer but a chemical called phenacetin that criminals use to 'cut' cocaine (dilute it) does
  kidney transplant - people who have a kidney transplant have an estimated 1 in 100 chance of developing kidney cancer in their remaining 'native' kidney
• people with kidney failure who require dialysis: dialysis is a treatment that is designed to replicate the functions of the kidneys - people who require dialysis are three times more likely to develop kidney cancer than the population at large