Cancer (AQA GCSE Biology): Revision Note

Cancer: Principles

• Cells in the body divide by mitosis to produce more cells – this is essential for growth and to replace cells that are lost or damaged

  • Cells of the intestines are constantly dividing to replace those that are shed as food moves through the digestive system

• Mitosis is just one part of the cell cycle which is regulated by many different genes to ensure that cells divide only when they need to and stop when required

• Cancer is caused as a result of changes in the DNA of cells that lead to uncontrolled growth and division – this can result in the formation of a tumour (a mass of cells)

  • Usually tumours form as a result of loss of control of the cell cycle

• Not all tumours are considered cancerous

• Benign tumours are growths of abnormal cells which are contained in one area, usually within a membrane

  • Crucially, benign tumours do not invade other parts of the body

• Malignant tumour cells are cancers

  • These cells invade neighbouring tissues and spread to different parts of the body via the blood and lymphatic system where they form secondary tumours

• Malignant tumours are more likely to disrupt the functioning of the organ they originate in (as they invade healthy tissue) and the organs they spread to

  • This is why tumour cells are dangerous and is how they lead to death

Lifestyle risk factors & cancer

• Anyone, at any age, can develop cancer, but increasing age and many lifestyle factors are associated with an increased risk of having cancer

• Treatments are constantly being developed, with targeted therapies and immunotherapy helping to improve survival rates for many different types of cancer

• Scientists have identified lifestyle risk factors for various types of cancer

• There are also genetic risk factors for many types of cancer; inheriting faulty genes can make individuals more susceptible to developing cancer

  • Individuals with faulty mismatch repair (MMR) genes responsible for proofing DNA are more likely to develop cancers of the bowel and reproductive systems

  • Individuals with faulty BRCA genes are more likely to develop breast and ovarian cancer than individuals with functioning BRCA genes