How cancer begins

Cancer begins with an alteration to the structure of DNA, which is found in all human cells. DNA provides our cells with a basic set of instructions such as when to grow and reproduce.

A change in its structure, called a genetic mutation, can alter these instructions and cause the cells to reproduce uncontrollably. This produces a lump of tissue known as a tumour.

How cancer spreads

Left untreated, cancer can quickly grow and spread to other parts of the body.

Cancer usually spreads through the lymphatic system. This is a series of glands (or nodes) located throughout the body, similar to the blood circulation system.

Lymph glands produce many specialised cells that your immune system needs to fight infection. Once the cancer reaches the lymphatic system, it can spread to any other part of your body, including your bones, blood and organs.

The human herpesvirus 8 (HHV-8)

Kaposi's sarcoma (KS) is caused by a virus called the human herpesvirus 8 (HHV-8), which is also known as the Kaposi's sarcoma-associated herpesvirus (KSHV).

It is thought that HHV-8 contains genetic material that interferes with the normal working of cells, causing them to reproduce in an uncontrollable manner.

HHV-8 does not cause Kaposi's sarcoma in everyone who contracts the virus. Instead, it only seems to cause Kaposi's sarcoma in:

• people who have an inherited (genetic) vulnerability to HHV-8, or
• people with a weakened immune system.

HHV-8 was first identified in 1994 but, as yet, there is no firm evidence as to how the virus is spread.

However, there is good circumstantial evidence that HHV-8 can be spread during unprotected anal sex. The rates of HHV-8 in specific countries show that the virus is almost always more widespread in the gay community than in heterosexuals.

There is circumstantial evidence that HHV-8 can be passed on through saliva. This means the virus could also be spread by kissing.