1.8
Name two types of tumour.
4
Explain why a tumour needs a blood supply.
5
What is the name of the type of tumour formed when a cancer spreads?
What triggers cancer? Chemicals and other agents that cause cancer are called carcinogens. Carcinogens cause cancer by damaging DNA. A change in the DNA of a cell is called a mutation. Mutations can also occur by chance as a cell is dividing.
Did you know? Many treatments for cancer come from plants, such as the Pacific yew and the Madagascan periwinkle. These drugs work by interfering with mitosis.
There are natural checks for such errors during the cell cycle. Some of our genes suppress developing tumours.
12000
Several mutations, not just one, are necessary to trigger cancer. This is why we are more likely to develop cancer as we get older.
10000
Mutations that lead to cancer can be caused by several agents:
8000
• • • • •
viruses (see Figure 1.30). chemicals in the home, industry or environment ionising radiation ultraviolet radiation lifestyle choices, such as alcohol intake or diet (see Figure 1.31).
6000 4000 2000
Annual number of cases in USA
3
mouth and throat
anus
25
vagina and vulva penis
cervix
Breast cancer death rate per 100 000 female population
30 0
HPV cases
20
non-HPV cases
Figure 1.30 Cancers caused by the human papilloma virus (HPV)
15
10
5
0 0
20
40
60 80 100 Animal fat intake (g/day)
120
140
160
Figure 1.31 Scattergraph showing the correlation between breast cancer deaths and animal fat intake. Each data point represents a different country. 6
Which type of cancer is caused only by HPV?
Google search: 'causes of cancer, carcinogen, detection of cancer, tumour'
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