What is Cancer?
Cancer is a disease of the cells, which are the body’s basic building blocks. Cancer occurs when abnormal cells grow in an uncontrolled way. These abnormal cells can damage or invade the surrounding tissues, or spread to other parts of the body, causing further damage.
Most cancers start in a particular organ; this is called the primary site or primary tumour. Tumours can be benign (not cancer) or malignant (cancer).
Benign tumours (not cancer)
Benign tumours do not spread outside their normal boundary to other parts of the body. Some benign tumours are precancerous and may progress to cancer if left untreated. Other benign tumours do not develop into cancer. However, if a benign tumour continues to grow at the original site, it can cause a problem by pressing on nearby organs.
Malignant tumours (cancer)
A malignant tumour is made up of cancer cells. When it first develops, this malignant tumour may be confined to its original site. This is known as a cancer in situ (or carcinoma in situ). If these cells are not treated, they may spread beyond their normal boundaries and into surrounding tissues, becoming invasive cancer.
How cancer spreads
Sometimes cancer cells break off the primary tumour, enter the bloodstream or lymphatic system, and travel to a new organ to form secondary tumours. This is called metastasis.
What are the different types of cancer?
There are many different types of cancer, and usually they are named for the organ or cell type of the primary cancer. For example, bladder cancer starts in the bladder, prostate cancer starts in the prostate, lung cancer starts in the lung.
Different types of cancer can be grouped into several broad categories2
carcinoma: cancer that begins in the skin or in tissues that line or cover internal organs for example, melanoma
sarcoma: cancer that begins in bone, fat, muscle, blood vessel, or other supportive or connective tissue - for example, osteosarcoma
leukaemia: cancer that begins in the tissues that make blood cells, such as the bone marrow - for example, acute myeloid leukaemia
lymphoma and myeloma: cancers that start in cells of the immune system - for example, Hodgkin lymphoma and multiple myeloma
central nervous system cancer: cancer that begins in the brain or spinal cord - for example, glioma.
What are the risk factors for cancer?
A risk factor is any factor that is associated with increasing someone’s chances of developing a certain condition, such as cancer. Some risk factors are modifiable, such as lifestyle or environmental risk factors, and others cannot be modified, such as family history and inherited factors.
Having one or more risk factors does not mean that a person will develop cancer. Many people have at least one risk factor but will never develop cancer, while others with cancer may have had no known risk factors. Even if a person with cancer has a risk factor, it is usually hard to know how much that risk factor contributed to the development of their disease.
For most cancers the causes are not fully understood. However, some factors that place individuals at a greater risk for cancer are well-recognised. Examples include:1
diet - for example, high intake of particular foods (such as processed meat and foods that are high in fat) is associated with an increased risk for some types of cancer
overweight and obesity
infections - for example, some types of human papillomavirus (HPV) infection can be associated with cervical and other cancers, and chronic hepatitis B or C infection can be associated with liver cancer
occupational exposure to agents, including chemicals, dusts and industrial processes
family history and genetic susceptibility - some genes that can predispose a person to cancer can be passed on from parent to child