Animal Tissues, Organs and Systems » Cancer

What is cancer?

Your body is made of trillions of cells, and many of them divide to replace old or damaged ones. This is normally carefully controlled. A cell divides when the body needs a new cell, and stops when it does not.

Sometimes a cell changes in a way that breaks this control. The changed cell grows and divides again and again, and the new cells do the same. Nothing tells them to stop. The result is a lump of cells called a tumour.

Key terms:

• Cancer: the result of changes in cells that lead to uncontrolled growth and division.
• Tumour: a lump of abnormal cells that have grown and divided out of control.

Cancer can start in almost any part of the body, such as the lungs, skin, breast or bowel. Not every lump is cancer, though. It depends on the type of tumour.

Benign tumours

A benign tumour is a growth of abnormal cells that stays in one area. It is usually held inside a membrane, a bit like a sealed bag. The cells do not invade other parts of the body.

Benign tumours are not cancers. They can still cause problems if they grow large enough to press on a nearby organ or blood vessel, so doctors may remove them. But they do not spread.

Malignant tumours

Malignant tumour cells are cancers. They behave very differently from benign cells:

• they invade neighbouring tissues, pushing into and damaging them
• cells break away and are carried to different parts of the body in the blood
• where these cells settle, they divide and form new tumours

The new tumours are called secondary tumours. The first tumour is the one where the cancer started. Spreading to new places makes cancer much harder to treat, because doctors have to deal with tumours in several parts of the body rather than one.

Key terms:

• Benign tumour: a growth of abnormal cells contained in one area, usually within a membrane, that does not invade other parts of the body.
• Malignant tumour: a cancer. Its cells invade neighbouring tissues and spread in the blood to form secondary tumours.
• Secondary tumour: a new tumour formed in another part of the body by cells that have spread from the first tumour.

Benign or malignant?

Risk factors for cancer

Scientists have studied large numbers of people to find out why some develop cancer and others do not. They have found two kinds of risk factor. Remember, a risk factor makes a disease more likely. It does not mean a person will definitely get it.

Lifestyle risk factors

Scientists have identified lifestyle risk factors for various types of cancer. Examples include:

• Smoking: linked to lung cancer and several other cancers.
• Obesity: linked to several types of cancer, including bowel cancer.
• Too much alcohol: linked to cancers such as liver and mouth cancer.
• Too much sunlight or sunbed use: the ultraviolet radiation is linked to skin cancer.

How carcinogens cause cancer is covered in Lifestyle and Non-Communicable Diseases. Here the key idea is that choices and habits can change a person's chance of getting cancer.

Genetic risk factors

There are also genetic risk factors for some cancers. Some people inherit faulty genes from their parents that make a particular cancer more likely. For example, inheriting certain faulty genes called BRCA1 and BRCA2 increases the risk of breast cancer. Cancer can run in some families for this reason.

Inheriting a faulty gene does not mean a person will definitely get cancer. It means the risk is higher than for the average person.

Exam-style question

A patient has a tumour in the bowel. Tests show that cells from the tumour have spread to the liver.

(a) Is this tumour benign or malignant? Give one reason for your answer. [2 marks]

(b) Name the tumour that forms in the liver. [1 mark]

(c) Describe how the cells reached the liver. [1 mark]

(d) Give one lifestyle risk factor and one genetic risk factor for cancer. [2 marks]