Cancer Information | Cancer Association Namibia

What is Cancer?

Cancer starts when cells change abnormally

Cancer begins when cells in the body start to grow and divide in an uncontrolled way. Normally, cells grow, divide and die in an organised and regulated process. When this process stops working properly, abnormal cells can continue to grow and form cancer.

Some cancers remain in one area of the body, while others can spread to different tissues and organs.

There are more than 200 different types of cancer, and statistics show that about 1 in 2 people will develop cancer during their lifetime. Thanks to ongoing medical research and improved treatments, many cancers can now be treated successfully.

How Cancer Begins

Changes in Cells

All cancers begin in cells. The human body is made up of around 100 trillion cells, which constantly grow, divide and replace older cells.

Normally, cells send signals to control when they should divide and when they should stop. When these signals fail, cells may begin to divide too often and grow into a mass of tissue called a tumour.

The place where cancer first develops is called the primary tumour.

Some cancers, such as leukaemia, begin in blood cells. These cancers do not form solid tumours but instead build up in the blood and bone marrow.

Gene Mutations

What are Gene Mutations?

For cancer to develop, changes must occur within the genes of a cell.
Genes normally control how cells grow, divide and function. Sometimes these genes become damaged or altered. These changes are called mutations.

by chance when cells divide
through natural processes in the body
because of external factors such as tobacco smoke or chemicals
due to inherited genetic changes from parents

Mutations can happen:

Usually several mutations are needed before a normal cell becomes a cancer cell.

These mutations can cause cells to:

produce too many growth signals
ignore signals that normally stop cell division
produce abnormal proteins that change how the cell behaves

Several mutations

Changes in Cells

All cancers begin in cells. The human body is made up of around 100 trillion cells, which constantly grow, divide and replace older cells.

Normally, cells send signals to control when they should divide and when they should stop. When these signals fail, cells may begin to divide too often and grow into a mass of tissue called a tumour.

The place where cancer first develops is called the primary tumour.

Some cancers, such as leukaemia, begin in blood cells. These cancers do not form solid tumours but instead build up in the blood and bone marrow.

How Cancer Begins

The Role of DNA

Inside every cell is a nucleus, which acts as the control centre. The nucleus contains chromosomes, which are made of thousands of genes.

Genes consist of DNA (deoxyribonucleic acid), the genetic code that instructs cells how to behave.

Genes tell a cell:

• what type of cell it should become

• when it should divide

• what functions it should perform

• when it should die

When these instructions become damaged, the cell can begin to grow uncontrollably.

How Tumours Grow

From Cells to Tumours

When cancer cells multiply repeatedly, they can form a tumour containing millions of cells.

At first, cancer cells often remain within the tissue where they started. Doctors call this carcinoma in situ or superficial cancer.

Eventually cancer cells may break through the basement membrane, the protective layer that keeps tissues organised. Once this happens, the cancer becomes invasive.

Benign versus Malignant Tumors

Benign tumours (non-cancerous)
grow slowly
do not spread to other parts of the body
are often surrounded by normal tissue
They may still cause problems if they:
grow very large
press on organs
cause pain or discomfort
produce hormones that affect the body
Malignant tumours (cancerous)
grow more rapidly
invade nearby tissues
can spread to other parts of the body
When cancer spreads to distant organs, this is called metastasis.

How Tumours Grow

From Cells to Tumours

When cancer cells multiply repeatedly, they can form a tumour containing millions of cells.

At first, cancer cells often remain within the tissue where they started. Doctors call this carcinoma in situ or superficial cancer.

Eventually cancer cells may break through the basement membrane, the protective layer that keeps tissues organised. Once this happens, the cancer becomes invasive.

Benign versus Malignant Tumors

diagram-showing-why-cancer-cells-need-their-own-blood-supply_0.jpg

Benign tumours (non-cancerous)

grow slowly
do not spread to other parts of the body
are often surrounded by normal tissue

They may still cause problems if they:

grow very large
press on organs
cause pain or discomfort
produce hormones that affect the body

Malignant tumours (cancerous)

grow more rapidly
invade nearby tissues
can spread to other parts of the body

When cancer spreads to distant organs, this is called metastasis.

Blood Supply and Cancer Growth

How Cancer
Spreads

Spread Through the Lymphatic System

How Tumours Get Nutrients

As a tumour grows, it needs oxygen and nutrients to survive. Cancer cells release signals called angiogenic factors, which stimulate the growth of new blood vessels. This process is called angiogenesis.

Without a blood supply, a tumour cannot grow much larger than the size of a pinhead.

Once new blood vessels develop, the tumour can grow faster.

Cancer cells can spread from the original tumour to other parts of the body.

This process happens in several steps:

• Cancer cells break away from the primary tumour

• They travel through the bloodstream or lymphatic system

• They settle in another organ

• They grow into a secondary tumour

These new tumours are called metastases.

The lymphatic system is a network of vessels and glands that helps fight infection and remove harmful substances from the body.

Cancer cells can enter nearby lymph vessels and travel to lymph nodes, where they may begin to grow into new tumours.

Doctors call this lymph node spread.

Spread Through the Bloodstream

Is Cancer
Genetic?

Important Genes Involved in Cancer

Cancer cells can also enter small blood vessels and travel through the bloodstream. These are called circulating tumour cells (CTCs).

Most cancer cells do not survive this journey. However, a few may settle in another organ and start forming a new tumour.

Common sites for metastases include:

• liver • lungs • bones • brain

Cancer develops because of changes in genes, but most cancers are not inherited.

Humans have about 25,000 genes, which contain the instructions for how cells behave.

Mutations in genes can occur due to:

• smoking • radiation • ultraviolet light from the sun

• environmental chemicals • substances in food

Sometimes people inherit faulty genes from their parents. This can increase their risk of developing certain cancers.

However, most cancers develop from gene changes that occur during a person’s lifetime.

Scientists have identified several types of genes that control cell division.

DNA repair genes

These genes repair damaged DNA. When they stop working properly, genetic errors can build up.

Oncogenes

These genes encourage cells to grow and divide. When they become overactive, they can cause uncontrolled cell growth.

Tumour suppressor genes

These genes normally slow down or stop cell division. If they become damaged, cells may continue growing when they should stop.

Self-destruction genes (apoptosis)

These genes tell damaged cells to die. If this process fails, abnormal cells may survive and develop into cancer.

What is Cancer?

How Cancer Begins

Gene Mutations

Mutations can happen:

Several mutations

How Cancer Begins

The Role of DNA

How Tumours Grow

Benign versus Malignant Tumors

How Tumours Grow

Benign versus Malignant Tumors

Blood Supply and Cancer Growth

How Cancer Spreads

Spread Through the Lymphatic System

Spread Through the Bloodstream

Is Cancer Genetic?

Important Genes Involved in Cancer

How Cancer
Spreads

Is Cancer
Genetic?