Cancer

• Cancers arise due to uncontrolled mitosis, dividing repeatedly and uncontrollably to form a tumour
• What are tumours?

  Groups of abnormal cells that form lumps or growths, which can start in any cell in the body
• How can tumours cause harm to the body?

  They can damage the organ in which the tumour is located, or other organs by exerting pressure and can cause blockages
• Malignant tumours are cancerous due to their rapid growth and their ability to invade and destroy surrounding tissues
• Cells within malignant tumours secrete chemicals that cause the formation of blood vessels to supply the tumour with nutrients
• What is metastasis?

  When cells break off malignant tumours and spread to other parts of the body through the bloodstream or lymphatic system
• When removed through surgery, malignant tumours can still grow back
• The formation of malignant tumours can be initiated by carcinogens
• What are carcinogens?

  Agents with the capacity to cause cancer
• What are some examples of carcinogens?

  Tobacco, asbestos and UV or X ray exposure
• Benign tumours are not cancerous, grow slowly and are not metastatic
• Benign tumours can cause harm to the body by forming blockages or putting pressure on the organ it is growing in or those surrounding it
• The formation of benign tumours can be initiated by inflammation, injury, diet and genetics
• Cancers start when the expression of genes that control cell division changes
• What is an oncogene?

  A mutated gene that causes cancer
• Mutations are common events and dont lead to cancer most of the time as most of them result in early cell death or the cell being destroyed by the body’s immune system
• Abnormal methylation of proto-oncogenes and tumour suppressor genes can cause abnormal cells that form growth and cancers to develop
• What are tumour suppressor genes?

  Normal genes that code for proteins that regulate the cell cycle
• Proteins coded for by tumour suppressor genes function by repairing DNA, slowing the cell cycle by ensuring checks are made and signal apoptosis when the cell is faulty
• Proteins coded for by tumour suppressor genes ensure that cells do not replicate if they contain mutated DNA or are faulty
• Why is it important that faulty or mutated cells dont replicate?

  They can lead to tumour formation
• Tumours develop when tumour suppressor genes are mutated or silenced
• Hypermethylation of DNA causes transcription inhibiting proteins to bind to the DNA, and if this occurs around tumour suppressor genes, it could result in tumour development
• Proto-oncogenes are normal genes that code for proteins that regulate cell growth and differentiation
• Proto-oncogenes can mutate to become oncogenes by carcinogens
• The mutation of proto-oncogenes into oncogenes can be caused by inversion or translocation mutation
• The inversion or translocation mutation of a proto-oncogene can lead to gene expression being unregulated and the protein produced by the gene being constantly activated
• Oncogenes are mutated genes that have the ability to cause cancer through the deregulation of the cell cycle
• How do oncogenes have the ability to cause cancer?

  They deregulate the cell cycle as it causes the proteins that stimulate growth and division to be constantly activated, which speeds up the cycle
• Proteins can be activated or deactivated through phosphorylation
• Phosphorylation is the addition of a phosphate group from ATP
• Binding to another protein or coenzyme, can change a proteins formation and potentially open up another binding site or reveal an active site
• Hypomethylation of proto-oncogenes causes them to act as oncogenes and produce proteins that encourage cell division, this stimulates cells to divide uncontrollably by mitosis and form tumours
• Increased exposure to oestrogen can increase the risk of developing breast cancer
• Why may some women be more exposed to oestrogen than others?

  Taking birth control, starting menstruation early and menopause late
• Oestrogen dependent breast tumours are seen when the tumours are categorised as oestrogen receptor positive
• Oestrogen is needed by some tumours to stimulate the expression of cell cycle genes that lead to growth and replication
• The cancer cells within oestrogen dependent breast tumours have oestrogen receptors that promote cell growth when stimulated by oestrogen
• The main treatment of oestrogen dependent breast tumours is a drug that acts as a competitive inhibitor to oestrogen as it is structurally very similar
• Competitive inhibitors permanently bind to oestrogen receptors, this stopting oestrogen from binding and therefore inhibiting the receptors action