7.2 Cancer

A free GCSE Biology lesson for AQA (8461) from OBA School: uncontrolled cell division, benign and malignant tumours, risk factors and treatment. Watch the video, read the explanation and worked examples, then try the revision questions. You can work through the full lesson, with every video, practice quizzes and printable worksheets with mark schemes, in our free online course.

What you will learn

• Describe cancer as the result of changes in cells that lead to uncontrolled growth and division
• Explain the difference between benign and malignant tumours
• Describe lifestyle and genetic risk factors for cancer
• Use data on cell division and survival rates

Key words

• Tumour: A mass of abnormal cells formed when cells divide in an uncontrolled way.
• Benign tumour: A growth of abnormal cells that stays in one place, usually within a membrane. It does not invade other tissues.
• Malignant tumour: A tumour that invades neighbouring tissues and can spread in the blood. Malignant tumours are cancers.
• Secondary tumour: A new tumour formed somewhere else in the body by cells that have broken off a malignant tumour.
• Mutation: A change in the DNA of a cell. Some mutations stop cells controlling their division.
• Carcinogen: Anything that increases the risk of cancer, such as chemicals in tobacco smoke or ionising radiation.

What is cancer?

Normally, body cells divide by mitosis only when new cells are needed for growth or repair. Cancer is the result of changes in cells (mutations in their DNA) that lead to uncontrolled growth and division. The extra cells form a mass called a tumour.

• Growth; Benign tumour contained in one area, usually within a membrane; Malignant tumour invades neighbouring tissues
• Spread; Benign tumour does not spread to other parts of the body; Malignant tumour cells break off, travel in the blood and form secondary tumours
• Is it cancer?; Benign tumour no (but can still be harmful, e.g. if it presses on the brain); Malignant tumour yes

Key fact: Benign tumours are not cancers, but they can still cause problems by pressing on organs. Malignant tumours are cancers.

Risk factors for cancer

Scientists have identified many risk factors that increase the chance of some cancers.

• Lifestyle; Examples smoking (lung, mouth, throat and many other cancers); obesity (bowel, liver, kidney and other cancers); drinking alcohol (mouth, throat, liver, breast); too much UV exposure from the sun or sunbeds (skin cancer)
• Carcinogens in the environment; Examples ionising radiation, such as radon gas or X-rays; chemicals such as asbestos
• Viral infection; Examples human papillomavirus, HPV (cervical cancer); hepatitis B (liver cancer)
• Genetic; Examples inherited faulty genes, e.g. faulty BRCA1 or BRCA2 alleles greatly increase the risk of breast and ovarian cancer

Exam tip: A risk factor increases the chance of cancer. Someone with a faulty BRCA gene may never develop cancer, and someone with no risk factors may still develop it.

Treating cancer and why early diagnosis matters

Treatments include surgery to remove a tumour, radiotherapy (ionising radiation aimed at the tumour) and chemotherapy (drugs that stop cells dividing). Radiotherapy and chemotherapy target cells that divide rapidly, so they can also damage healthy fast-dividing cells, causing side effects such as hair loss and sickness.

Finding a cancer before it spreads makes treatment much more likely to succeed. That is why screening programmes and checking for unusual lumps or moles are so important.

Worked example: how fast a tumour grows

A cancer cell divides every 4 days, and so do all its daughter cells. Starting from one cell, how many cells are there after 28 days?
number of divisions = 28 ÷ 4 = 7
each division doubles the number of cells: 2⁷ = 128

Answer: 128 cells. After 30 doublings there would be over 1 000 000 000 cells (2³⁰ ≈ 1.07 × 10⁹).

Common mistakes

• Saying all tumours are cancer. Only malignant tumours are cancers.
• Saying cancer cells "divide by meiosis". They divide by mitosis, but out of control.
• Saying cancer is caught from other people. Cancer is non-communicable, although some viruses (HPV) can trigger it.
• Saying cancer cells "spread through the body" without saying how: they travel in the blood (or lymph) and form secondary tumours.

Revision questions

Try these, then check your answers below each one.

Question 1. What is cancer the result of? (Choose from: Infection by bacteria, Cells dividing by meiosis, Changes in cells that lead to uncontrolled growth and division, A lack of vitamins in the diet.)

Answer: Changes in cells that lead to uncontrolled growth and division

Working: Cancer results from changes (mutations) in cells that lead to uncontrolled growth and division.

Question 2. True or false? Benign tumours are cancers.

Answer: False

Working: False. Only malignant tumours are cancers.

Question 3. A tumour cell divides every 5 days, and so do all its daughter cells. Starting with one cell, how many cells are there after 40 days?

Answer: 256

Working: 40 ÷ 5 = 8 divisions. 2⁸ = 256 cells.

Related lessons

• Previous lesson: 7.1 Non-Communicable Diseases
• Next lesson: 7.3 Smoking and the Risk of Disease
• In this chapter: 7.4 Diet, Exercise, and Disease
• In this chapter: 7.5 Alcohol and Other Carcinogens

Continue in the full course

This lesson is section 7.2 (AGCBH0702) of our free GCSE Biology course for AQA. In the full course you get every video for this section, a self-marking practice quiz, a printable worksheet with a mark scheme, chapter tests, and your progress saved. Go to the full GCSE Biology course.