5-1-replication-and-division-of-nuclei-and-cells AS how-tumours-form

How a tumour forms

• Cancers demonstrate how important it is that cell division is precisely controlled, as cancers arise due to uncontrolled mitosis

• Cancerous cells divide repeatedly and uncontrollably, forming a tumour (an irregular mass of cells)

• Cancers start when changes occur in the genes that control cell division

• A change in any gene is known as a mutation

  • If the mutated gene is one that causes cancer, it is referred to as an oncogene

    • Mutations are common events and don’t lead to cancer most of the time

    • Most mutations either result in early cell death or result in the cell being destroyed by the body’s immune system

    • As most cells can be easily replaced, these events usually have no harmful effect on the body

• The mutations that result in the generation of cancerous cells do not result in early cell death or in the cell being destroyed by the body’s immune system

  • This means that the harmful mutation occurring in the original cell can be passed on to all that cell’s descendants

• Carcinogens are any agents that may cause cancer (e.g. UV light, tar in tobacco smoke, and X-rays)

  • If the agent causes cancer it is described as carcinogenic

Benign vs malignant tumours

• Some tumours (such as warts) do not spread from their original site – these are known as benign tumours and do not cause cancer

• Some tumours spread through the body, invading and destroying other tissues – these are known as malignant tumours and cause cancer

  • Malignant tumours interfere with the normal functioning of the organ / tissue in which they have started to grow (e.g. they may block the intestines, lungs, or blood vessels

  • Malignant tumour cells can break off the tumour and travel through the blood and / or lymphatic system to form secondary growths in other parts of the body

  • The spreading of cancers in this way is known as metastasis

  • Metastasis is very dangerous as it can be very difficult to detect, locate, and remove secondary cancers