biology

• Cancer


  A disease characterized by uncontrolled cell growth

  
• Cancer


  • Most cancers are a result of a cell accumulating mutations that ultimately cause a loss of control over the cell cycle

  
• The nuclei of cancer cells are enlarged and may contain an abnormal number of chromosomes

  
• Carcinogenesis


  1. Initiation: A single cell undergoes mutation and divides repeatedly

  2. Promotion: A tumor develops, and the tumor cells continue to divide. As they divide, they undergo mutations

  3. Progression: One cell undergoes a mutation. This process is repeated several times; eventually there is a cell that has the ability to invade surrounding tissues

  
• Cancer cells compete with normal cells for food and oxygen, until the normal starve to death and disrupt the homeostasis

  
• Metastasis


  The spread of cancer cells to other parts of the body

  
• Checkpoint proteins


  Proteins that control progression of the cell cycle, especially those that limit replication of cells containing damaged DNA
• Mutations in checkpoint proteins cause the cell to lose control of the cell cycle, resulting in cancer

  
• Common cancers


  • Respiratory-Lung cancer due to smoking
  • Skin cancer
• Carcinogen


  A chemical that causes cancer
• Carcinogens

  • Tobacco smoke
  • Asbestos
• Tobacco smoke contains a number of organic chemicals that are known carcinogens, including N-nitrosonornicotine, vinyl chloride, and benzo[a]pyrene
• The greater the number of cigarettes per day and the earlier the habit starts since teenager years, the more likely it is that cancer will develop
• About 80% of all cancers, including oral cancer, cancers of the larynx, eusophagus, pancreas, bladder, kidney, and cervix, are related with smoking
• When smoking is combined with drinking alcohol, the risk of these cancers increases
• Asbestos


  A natural mineral carcinogen often used in many construction products
• Damaged asbestos may release asbestos fibers and become a health hazard. Inhalation of asbestos fibers has been linked to an increased risk of lung cancer
• At least four types of DNA viruses—hepatitis B and C viruses, Epstein–Barr virus, and human papillomavirus (HPV)—are believed to cause human cancers

  
• Chemotherapy


  Cancer treatment using drugs to kill cancer cells
• Chemotherapeutic drugs

  • Kill cells by damaging their DNA or interfering with DNA synthesis
  • The hope is that all cancer cells will be killed, while leaving enough normal cells

  
• Examples of chemotherapeutic drugs

  • Alkylating agents: Interfere with the growth of cancer cells by blocking the replication of DNA
  • Antimetabolites: Block the enzymes needed by cancer cells to live and grow
  • Antitumor antibiotics: Interfere with DNA, blocking certain enzymes and cell division and changing plasma membranes
  • Mitotic inhibitors: Inhibit cell division or hinder certain enzymes necessary in the cell reproduction process
  • Nitrosoureas: Impede the enzymes that help repair DNA

  
• Chemotherapy sometimes fails and cancer cells become resistant to one or several chemotherapeutic drugs, a phenomenon called multidrug resistance
• Multidrug resistance occurs because a plasma membrane carrier pumps the drug (or drugs) out of the cancer cell before it can be harmed

  
• Solution to multidrug resistance

  Combinations of drugs with different toxic activities, because cancer cells can't become resistant to many different types at once

  
• Certain types of cancer, such as leukemias, lymphomas, and testicular cancer, are now successfully treated by combination chemotherapy alone
• The survival rate for children with childhood leukemia is 80%
• Hodgkin's disease, a lymphoma, once killed two out of three patients. Combination therapy, using four different drugs, can now wipe out the disease in a matter of months. Three out of four patients achieve a cure, even when the cancer is not diagnosed immediately