How does cancer begin?

Cancer begins with an alteration to the structure of 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, known as a tumor.

How does cancer spread?

Cancer is known to affect two specific genes known as the:

• oncogene, and
• tumor suppresser gene.

The oncogene is responsible for encouraging cell growth. Cancer seems to cause the oncogene to go into 'overdrive' so that the cells grow and multiply at a faster rate.

Cancer also deactivates the tumor suppresser gene. This gene is designed to regulate cell growth by making sure that cells only reproduce when needed.

The combination of the overactive onocgene, and the deactivated tumor suppressor gene means that the cancer can quickly grow and spread to the other parts of the body, usually via the lymphatic system.

The lymphatic system is a series of glands (or nodes) that are spread throughout your body, much like your blood circulation system. These glands produce many of the specialized cells needed by your immune system.

Once the cancer reaches the lymphatic system it is capable of spreading to any other part of your body, including your bones, blood, and organs.

What causes cancer?

Cancer can be caused by:

• carcinogens - chemicals that are known to cause the mutations associated with cancer, including alcohol and tobacco,
• exposure to a significant amount of radiation ,
• infectious diseases such as the human papillomavirus (HPV),
• hormonal imbalance which can occur during the menopause, and
• conditions that affect the immune system , such as HIV.

Some types of cancer can run in families. For example, your risks of developing certain types of breast, or ovarian, cancer are higher if you have a close relative who developed the condition.

Diet and lifestyle are also important factors in the development of cancer. People who get regular exercise, eat a healthy, balanced diet, and are a healthy weight, have a lower risk of developing cancer. However, not taking exercise, eating a high fat diet, and being obese increases your chances of developing cancer.

Specific causes of cancer are discussed below.

Carcinogens

It is known that exposure to certain chemicals can cause the mutations that lead to cancer. The most common carcinogen is tobacco smoke, which can cause lung and bladder cancer. Excessive alcohol consumption can also cause cancer, as can exposure to asbestos fibers.

Radiation

Exposure to significant levels of radiation can cause cancer. This includes over-exposure to sunlight, or over-use of tanning beds, or lamps; all of which can cause skin cancer.

However, not all forms of radiation are dangerous. For example, the amount of radiation that is used by X-rays, or radiography machines, is small and will not cause you any harm.

Infectious diseases

Many viral infections can damage cells and cause cancer. The most common infectious conditions known to cause cancer are outlined below.

• Human Papilloma Virus (HPV) , which is responsible for 95% of all cases of cervical cancer.
• hepatitis B and hepatitis C , both of which can cause liver cancer.
• Epstien-Barr virus , which is responsible for glandular fever, and has been linked to an increased risk of developing Hodgkin's lymphoma, which is a cancer of the lymphatic system.
• Human T-lymphotropic virus , which is blood-borne virus that is rare in the US but common in other parts of the world, such as Japan and Africa and is known to cause leukemia.

Hormonal imbalance

It is thought that changes in hormone levels can trigger cancerous cell growth in a similar way to exposure to carcinogens. This is why breast cancer is more common in post-menopausal women, as the menopause causes a change of the levels of the hormone, estrogen, in the body.

Conditions that affect the immune system

Certain cancers, such as Karposi's sarcoma, and lymphoma, are common in people whose immune system is not functioning properly due to a medical condition, such as HIV.