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What is cancer?

Cancer is the umbrella term given to a group of more than 200 diseases that are caused when abnormal cells divide and multiply in an uncontrolled way, causing damage to normal tissues.

15 January 2016

According to the World Health Organization (WHO), cancers are among the leading causes of morbidity and mortality worldwide. The WHO adds that around one-third of cancer deaths are due to the five leading behavioural and dietary risks, which are high body mass index, low fruit and vegetable intake, lack of physical activity, tobacco use and alcohol use.

What are cancer cells?

There are trillions of living cells in our body. Normal cells grow, divide and die as part of their life cycle. During our developmental years, normal cells divide faster to allow our bodies to grow. Once we’re adults, most cells divide only to replace worn-out or dying cells or to repair damage.

There’s an intricate network of signals at work that determines just how much of each type of cell is needed. Abnormal or cancer cells don’t follow this life cycle; instead of dying, they continue to grow and divide, producing more abnormal cells. These cells may invade and grow into other tissue – something normal cells don’t do.

How do cells become abnormal?

Abnormal cell growth stems from damage to the DNA of that cell that cannot be repaired. The damaged cell continues to divide creating more cells that the body doesn’t need and these all have the same DNA damage. People may inherit faulty DNA from a parent; damage may occur during the cell’s life cycle; or from obvious external environmental factors such as sun exposure and smoking, but more often than not, it is difficult to know what causes any one person’s cancer.

Over time, the uncontrolled cells may form tumours that can invade nearby normal tissue, including vital organs. Some cancers rarely form solid tumours, like leukaemia, where cells build up in the blood and bone marrow.

How does cancer spread?

Cancer cells can travel to other parts of the body via the bloodstream and lymph vessels where they can continue to grow and form tumours, crowding out or damaging healthy tissue or organs. This process is known as metastasis. However, the cancer is always named from the place it originated. Colon cancer that has spread to the liver is called metastatic colorectal cancer – also known as colon cancer – not liver cancer.

The difference between benign and malignant tumours

A tumour is a lump or growth of tissue made up of abnormal cells.

If you are told you have a benign tumour, it means it is non-cancerous. They usually grow slowly, do not spread and do not invade other tissue. While not usually life threatening, they may cause problems by creating pressure on surrounding tissue. Cells in benign tumours tend to be similar to normal cells, and usually grow surrounded by normal cells that surround them.

Malignant tumours are cancerous. They may form much more quickly than benign tumours do, but in order to grow they need a blood supply for oxygen for new and dividing cells. Cancer cells produce chemicals that stimulate tiny blood vessels to grow around them, branching off from existing blood vessels (a process called angiogenesis).

Malignant cells have the ability to push through or between normal cells, so as they divide and multiply, these cells invade and damage the surrounding tissue.

Different types of cancers

In South Africa, the most common cancers affecting women are breast cancer, cervical cancer,colorectal cancer, lung cancer and oesophageal cancer. For men, they are lung cancer, oesophageal cancer, prostate cancer, liver cancer and stomach cancer. This information is based on figures released by the South African Medical Research Council www.mrc.ac.za

There are more than 200 different types of cancers, with each type classified by the type of cell the cancer originated from.

Generally, they fall into one of three categories:

  1. Carcinomas: Cancer that arises from cells that line a body surface or the lining of a gland, for example, the skin, the lining of the oesophagus, mouth, airways and cervix.
  2. Sarcomas: Cancer that arises from cells that make up connective tissue, such as bones or muscles.
  3. Leukaemias and lymphomas: These arise from cells in the bone marrow and lymph glands.

For more information

CHOC Childhood Cancer Foundation SA: www.choc.org.za or call (011) 326-1717

The South African Childhood Cancer Study Group: www.saccsg.co.za

Cancer Association of South Africa: www.cansa.org.za (CANSA offers support to parents of children who have been diagnosed with cancer. Email [email protected] to find out more about their TLC Support Groups.)

Read More: Cancer Super Section