5.3 Cancer

• What is the primary cause of cancer?

  Mutation or abnormal activation of genes
• What do proto-oncogenes code for?

  Proteins that control cell adhesion and growth
• What happens when proto-oncogenes are mutated?

  They can become oncogenes causing cancer
• How many different oncogenes have been discovered in human cancers?

  As many as 100 oncogenes
• What are antioncogenes also known as?

  Tumor suppressor genes
• What is the role of antioncogenes?

  They suppress the activation of oncogenes
• What can lead to cancer regarding antioncogenes?

  Loss or inactivation of antioncogenes
• Why do most mutated cells not lead to cancer?

  They often have less survival capability
• What happens to most mutated cells that survive?

  They still have normal feedback controls
• How does the immune system respond to potentially cancerous cells?

  It forms antibodies or sensitized lymphocytes
• How much does cancer probability increase in immunosuppressed individuals?

  Multiplied as much as fivefold
• What is usually required to cause cancer?

  Presence of several activated oncogenes
• What might one activated oncogene do?

  Promote rapid reproduction of a cell line
• What is the role of DNA replication in preventing cancer?

  It ensures precision and repairs abnormal strands
• How often does a newly formed cell have significant mutant characteristics?

  One in every few million cells
• What are the main reasons mutated cells do not lead to cancer?

  • Most mutated cells die quickly
  • Few surviving cells become cancerous
  • Immune system destroys potential cancer cells
  • Multiple oncogenes usually needed for cancer
• What processes help maintain DNA integrity before mitosis?

  • Precise DNA replication
  • Proofreading and repair of abnormal strands
• What is required for mutations to take place?

  Chance alone
• How can the probability of mutations be increased?

  By exposure to certain factors
• What types of radiation can predispose individuals to cancer?

  • Ionizing radiation (x-rays, gamma rays)
  • Particle radiation from radioactive substances
  • Ultraviolet light
• What happens to DNA strands under ionizing radiation?

  They can rupture, causing mutations
• What are chemical substances that cause mutations called?

  Carcinogens
• What is the risk for workers in chemical plants producing aniline dye derivatives?

  They have a special predisposition to cancer
• What percentage of cancer deaths are caused by carcinogens in cigarette smoke?

  About one quarter
• How can physical irritants lead to cancer?

  By causing rapid mitotic replacement of cells
• What is a consequence of rapid mitosis?

  Greater chance for mutation
• What is the hereditary tendency to cancer based on?

  Mutations in the inherited genome
• Why do families predisposed to cancer require fewer additional mutations?

  They may already have mutated genes
• What types of viruses can cause cancer in laboratory animals?

  DNA and RNA viruses
• How do DNA viruses cause cancer?

  By inserting their DNA into chromosomes
• What role does reverse transcriptase play in RNA viruses?

  It transcribes DNA from RNA
• What happens to the transcribed DNA from RNA viruses?

  It inserts into the animal cell genome
• What is a major difference between cancer cells and normal cells?

  Cancer cells do not respect growth limits
• Why do cancer cells not require the same growth factors as normal cells?

  They presumably do not need all growth factors
• How do cancer cells differ in adhesion compared to normal cells?

  Cancer cells are less adhesive to each other
• What is the consequence of cancer cells being less adhesive?

  They wander through tissues and enter the bloodstream
• What do cancer cells form when they spread throughout the body?

  They form nidi for new cancerous growths
• What do some cancers produce to support their growth?

  Angiogenic factors for new blood vessels
• What is the role of new blood vessels in cancer growth?

  They supply nutrients required for cancer growth
• Why do cancer cells kill normal tissues?

  They compete for nutrients with normal tissues