Uncontrolled Cell Division & Tumour Formation (HL) (HL IB Biology)

• Mutations of the genes that control the cell cycle may lead to cancer
• Two types of genes are typically involved with the development of cancer:
  • Proto-oncogenes code for proteins which stimulate normal cell division
    • These genes are converted to oncogenes once they mutate
    • This results in an increase in the protein product produced or proteins which are permanently activated
    • Leading to uncontrolled cell division which may result in cancer
  • Tumour-suppressor genes code for proteins which inhibit cell division or promote controlled cell death (known as apoptosis) should the nucleus contain damaged DNA
    • Mutations in these genes may result in no or reduced protein product or proteins which are permanently deactivated
    • Leading to uncontrolled cell division and possibly cancer

• 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)
• A typical tumour contains around a thousand million cancerous cells by the time it is detected

Types of tumour

• Tumours have different characteristics depending on whether they are cancerous (malignant) or non-cancerous (benign)
• All tumours may cause harm to the body by:
  • Damaging the organ in which the tumour is located
  • Causing blockages or obstructions
  • Damaging other organs by exerting pressure

Malignant tumours

• Malignant tumours are cancerous
• Malignant tumours cause cancer by growing rapidly, then invading and destroying surrounding tissues
  • Cells within malignant tumours secret chemicals that cause the formation of blood vessels to supply the tumour with nutrients, growth factors and oxygen
  • These tumours are known as primary tumours and this is where cancer starts to develop
• Cells can break off these primary tumours and spread to other parts of the body through the bloodstream or lymphatic system, this is called metastasis
  • Metastasis causes the spread of tumours to other places in the body, affecting multiple organs
  • Tumours that develop from cells that broke off the primary tumour are known as secondary tumours
  • When removed through surgery, malignant secondary tumours can still grow back
• The formation of malignant tumours can be initiated by carcinogens such as:
  • UV or X-ray exposure
  • Tobacco from cigarettes
  • Asbestos
  • Processed meat

Cancer formation diagram

Stages in the development of cancer

Benign tumours

• Benign tumours are not cancerous
• These tumours grow slowly 
• Benign tumours do not invade other tissues and do not metastasise, unlike malignant tumours
• These tumours can cause damage such as blockages or by exerting pressure on the organ it is growing in or those surrounding it
• When removed, benign tumours do not usually grow back
• The formation of benign tumours can be initiated by:
  • Inflammation or infection
  • Injury
  • Diet
  • Genetics
  • Toxins and radiation
• Examples of benign tumours are:
  • Polyps found in the nose, colon and ovaries
  • Non-cancerous brain tumours
  • Warts, caused by a viral infection