Biology
Cancer
Key words
Learning objectives:
benign carcinogen malignant mutation secondary tumour
• describe cancer as a condition resulting from changes in cells that lead to their uncontrolled growth, division and spread • understand some of the risk factors that trigger cells to become cancerous.
Every year, over 300 000 people in the UK are diagnosed with cancer. It is estimated, however, that four in ten cases of cancer could be prevented by lifestyle changes.
What is cancer? Normally, cells grow and divide by mitosis when the body needs new cells to replace old or damaged cells. When a cell becomes cancerous, it begins to divide uncontrollably. New cells are produced even though the body does not need them. The extra cells produced form growths called tumours. Most tumours are solid, but cancers of the blood, for instance leukaemia, are an exception. 1
What is cancer?
2
Name one type of cancer that does not form a solid tumour.
Figure 1.28 A CT scanner, used to detect cancer
Types of tumour Type of tumour
Characteristics
Benign
• slow growing • often have a capsule around them, so can be removed easily • not cancerous and rarely spread to other parts of the body • they can press on other body organs and look unsightly.
Malignant
• grow faster • can spread throughout other body tissues • as the tumour grows, cancer cells detach and can form secondary tumours in other parts of the body.
Malignant cells develop.
The tumour secretes hormone-like chemicals.
The malignant cells divide and can invade normal tissues.
Blood vessels are stimulated to grow around the tumour; the blood vessels supply the tumour with food and oxygen.
Malignant cells detach from the tumour and are transported away in the blood.
Malignant cells can detach from the tumour and spread to other parts of the body.
The malignant cell squeezes through the capillary wall.
The cell divides to produce a secondary tumour.
Figure 1.29 The growth and spread of a tumour
28
AQA GCSE Biology for Combined Science: Trilogy: Student Book
75047_P012_047.indd 28
5/20/16 10:08 AM