8.2.11

Tumours

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Types of Tumour

Tumours are a cluster of cells that are growing uncontrollably. In some cases, tumours can cause cancer. There are two types of tumour:

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Benign tumours

  • Benign tumours are NOT cancerous.
  • Benign tumours consist of cells that are dividing uncontrollably but the cells cannot spread and invade other tissues.
  • Benign tumours can develop into malignant tumours.
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Malignant tumours

  • Malignant tumours are cancerous.
  • Malignant tumours consist of cells that are dividing uncontrollably and spread into other tissues and around the body.
  • Malignant tumours can be life-threatening and can grow rapidly.

Development of Tumours

Tumours can develop when gene expression is not regulated correctly. The development of tumours can happen in the following ways:

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Tumour suppressor genes

  • Tumour suppressor genes are genes found in all cells.
    • These genes inhibit cell division to regulate the rate at which cells divide.
  • Increased methylation of a tumour suppressor gene inhibits this gene.
    • When tumour suppressor genes are not expressed, cell division is not inhibited. This causes the cells to divide uncontrollably.
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Oncogenes

  • Oncogenes are mutations in a gene called a proto-oncogene. Oncogenes are capable of transforming a cell into a cancerous cell because they cause excessive cell division.
  • Proto-oncogenes normally stimulate cell division.
  • Decreased methylation of a proto-oncogene causes proto-oncogenes to be over-expressed.
    • Over-expression of proto-oncogenes stimulates cell division.
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Oestrogen

  • Oestrogen is a hormone that can bind to receptors on transcription factors in the cytoplasm.
  • Oestrogen can increase the expression of genes.
    • When genes are over-expressed, a tumour may develop.
  • High levels of oestrogen have been detected in some breast cancers.

Jump to other topics

1Biological Molecules

2Cells

3Substance Exchange

4Genetic Information & Variation

5Energy Transfers (A2 only)

6Responding to Change (A2 only)

7Genetics & Ecosystems (A2 only)

8The Control of Gene Expression (A2 only)

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