Cancer: Tumours and Risk Factors

Cancer is the result of changes in cells that lead to uncontrolled growth and division.

In a healthy body, mitosis — the cell division that produces new identical cells for growth and repair — is tightly controlled. Cells only divide when more cells are needed, and they stop when they are not. Cancer begins when that control breaks down: a cell starts to divide again and again without stopping, even when no new cells are required.

Normal cells	Cancer cells
Divide by mitosis only when new cells needed	Divide continuously, even when not needed
Stop dividing once a tissue is the right size	Keep dividing without stopping
Growth is controlled	Growth is uncontrolled

This uncontrolled division produces a mass of extra cells. That mass is called a tumour.

Cancer is caused by changes in cells that lead to uncontrolled growth and division, producing a tumour.

The single most important idea to carry through this lesson is that the root problem is mitosis happening out of control. Everything else — tumours, spreading, risk factors — follows from that one change inside the cell.

There are two types of tumour, and the difference between them is the whole basis of this topic. The first type is benign.

A benign tumour is a growth of abnormal cells that is contained in one area, usually within a membrane. The membrane holds the mass together so the abnormal cells stay where they formed. A benign tumour does not invade other parts of the body.

Because the cells stay put, a benign tumour grows by pushing against the tissue around it rather than spreading through it. Examples include many warts and some types of mole. These growths are usually not dangerous — although a benign tumour can still cause problems if it grows large and presses on a nearby organ, such as a brain tumour pressing on surrounding tissue inside the skull.

A benign tumour: abnormal cells contained in one area, usually within a membrane, that do not invade other tissues or spread around the body.

Key features to remember for the exam:

• Grows in one place
• Usually enclosed within a membrane
• Does not invade neighbouring tissues
• Does not spread to other parts of the body

The second type of tumour is malignant — and malignant tumour cells are cancers. This is the type that makes cancer dangerous.

A malignant tumour does two things a benign tumour does not. First, its cells invade neighbouring tissues, growing into and damaging the healthy tissue around them rather than staying contained. Second, cells can break away and spread to different parts of the body in the blood.

When malignant cells travel in the blood, they can settle in a new part of the body and start dividing there, forming a new tumour. These new growths are called secondary tumours.

Malignant tumour cells are cancers. They invade neighbouring tissues and spread to different parts of the body in the blood, where they form secondary tumours.

(Extra context — the spread of cancer cells from a primary tumour to form secondary tumours elsewhere is called metastasis. The term is beyond AQA 8461, but it names the process the spec describes.)

It is the ability to invade and to spread in the blood that makes malignant tumours life-threatening, because secondary tumours can damage several organs at once.

The comparison between the two tumour types is the most heavily tested part of this topic. Learn this table in both directions — you should be able to state a feature and give the type, or be given the type and state the feature.

Feature	Benign tumour	Malignant tumour
Cause	Uncontrolled cell division	Uncontrolled cell division
Location	Stays in one area	Invades neighbouring tissues
Membrane	Usually contained within a membrane	Not contained — grows into surrounding tissue
Spreads in the blood?	No	Yes
Forms secondary tumours?	No	Yes
Is it a cancer?	No	Yes — malignant cells are cancers
Usual danger level	Often not dangerous	Dangerous / life-threatening

Notice the one thing both share: both are caused by uncontrolled cell division. The difference is entirely about behaviour — whether the cells stay put or invade and spread.

Exam shortcut: if a tumour invades, spreads in the blood, or forms secondary tumours, it is malignant (a cancer). If it is contained in one place within a membrane, it is benign.

These walk-throughs show how to apply the two definitions to the kind of description an exam question gives you. Match each feature to the correct type and justify your answer.

Example 1 — Classify from a description.

A patient has a mass of abnormal cells that is enclosed in a membrane, has stayed in the same place since it was found, and shows no sign of spreading to other organs.

This tumour is benign. Justification: it is contained within a membrane and stays in one area with no spread to other parts of the body — these are exactly the features of a benign tumour. Because the cells are not invading or spreading, it is not a cancer.

Example 2 — Classify and explain the danger.

A patient has a tumour whose cells have grown into the surrounding tissue, and identical abnormal cells have since been found in the liver and the lungs.

This tumour is malignant — a cancer. Justification: the cells have invaded neighbouring tissues, and identical cells appearing in distant organs (liver and lungs) show the cells have spread in the blood and formed secondary tumours. A benign tumour cannot do either of these things.

When a question gives you tumour features, do not just label it — quote the feature that proves your choice. "Malignant, because the cells have spread in the blood to form secondary tumours" earns the reasoning marks; "malignant" alone does not.

The same logic works in reverse. If told a tumour is malignant, you are expected to state that its cells invade neighbouring tissues and can spread in the blood to form secondary tumours elsewhere in the body.

Scientists have identified risk factors for various types of cancer. A risk factor is something that increases the chance of developing a cancer — it does not guarantee it. The factors fall into two groups, and you should know both.

Genetic risk factors. There are genetic risk factors for some cancers. Some people inherit faulty versions of genes that make their cells more likely to begin dividing uncontrollably, raising their risk of certain cancers compared with the general population.

Lifestyle and environmental risk factors. Scientists have identified lifestyle risk factors for various types of cancer. Many of these involve carcinogens — substances or types of radiation that can cause cancer by damaging the genetic material inside cells.

Carcinogen / risk factor	Linked cancer (example)
Ionising radiation (e.g. X-rays, radon, nuclear radiation)	Various cancers
Chemicals in tobacco smoke	Lung cancer
UV radiation from the Sun / sunbeds	Skin cancer

A carcinogen is an agent that can cause cancer. Ionising radiation and the chemicals in tobacco smoke are carcinogens named in the AQA specification.

How a carcinogen leads to a tumour, step by step:

1. A carcinogen (such as UV light or chemicals in tobacco smoke) damages the genetic material inside a cell.
2. The damage changes the cell so its division is no longer controlled.
3. The cell begins to divide uncontrollably by mitosis.
4. This uncontrolled division builds a tumour, which may be malignant.

This is the through-line of the whole topic: a risk factor causes a change in a cell, that change makes division uncontrolled, and uncontrolled division forms a tumour.

(Extra context — carcinogens and ionising radiation, along with diet, alcohol and obesity, are listed by AQA 8461 under non-communicable disease risk factors (section 4.2.2.6). Section 4.2.2.7 itself only requires that lifestyle and genetic risk factors for cancer exist; the named carcinogens above come from the related section.)

1. Saying benign tumours never cause any harm

Benign tumours do not invade or spread, but a large one can still press on nearby organs and cause problems. "Benign" means it stays in one place, not that it is always harmless.

2. Forgetting that malignant cells spread in the blood

The spec is specific: malignant cells spread to other parts of the body in the blood, where they form secondary tumours. State the blood as the route — do not just say they "move around".

3. Mixing up which type is the cancer

Malignant tumour cells are the cancers. Benign tumours are not cancers. A common error is to call any tumour "cancer" — only malignant ones qualify.

4. Confusing primary and secondary tumours

The original tumour is the primary tumour. A secondary tumour forms when cells spread in the blood and start dividing in a new location. Secondary tumours are a feature of malignant cancers only.

5. Treating a risk factor as a guaranteed cause

A risk factor increases the chance of cancer; it does not guarantee it. Not everyone exposed to a carcinogen develops cancer, and some people with no obvious risk factors still do.

6. Forgetting genetic risk factors

Cancer risk is not only about lifestyle. Some cancers have genetic risk factors — inherited faulty genes — and a full answer on risk factors should mention both genetic and lifestyle/environmental causes.