MED3ATA Cancer Biology

• Tumor


  An abnormal growth when a cell proliferates more than it normally would, resulting in a lump of cells in a particular organ
• Benign tumor


  Localized, not invasive, cells stay in one spot and do not affect the function of the organ too much
• Malignant tumor


  Acquired the capacity to invade into the normal tissue, spreading and migrating within the organ
• Metastasis


  Cells from a tumor acquire the ability to get into the blood or lymph system and spread to other parts of the body
• Cancer


  Unregulated growth that is invasive and capable of spreading within one organ or to other parts of the body
• Phases of cancer development

  1. Genetic changes enable excessive cell division (hyperplasia)

  2. Cells acquire altered morphology (dysplasia)

  3. Cells acquire invasive ability (invasive cancer)

  4. Cells acquire ability to enter blood/lymph and spread (metastasis)
• Cancer is a disease of multicellular organisms, where cells go rogue and prioritize their own survival and proliferation over the organism
• Cancers are particularly common in vertebrates, especially humans, and have affected humans for a long time
• Features used to classify cancers

  • Cell type or organ of origin
  • Size of tumor and extent of spread (stage)
  • Growth rate (chronic or acute)
  • Microscopic appearance and cell division (grade)
  • Molecular features (e.g. receptor expression)
• Carcinomas


  Cancers that originate from cells that were originally part of the ectoderm or endoderm, more common than sarcomas
• Sarcomas


  Cancers that derive from mesoderm-derived cells, less common and more common in children
• Leukemias


  Cancers of blood cells, can arise in bone marrow or in circulating blood cells
• Lymphomas


  Cancers generated from lymphoid cells, commence in lymph nodes, spleen, tonsils or thymus
• Grading


  Pathologist examines tumor sample under microscope to assess how similar or different it looks to normal tissue, low grade is more similar, high grade is less differentiated
• Staging


  Assesses the size of the tumor and extent of spread, important for prognosis and treatment
• Tumor grading


  Process where a pathologist examines a tumor sample under a microscope and assigns a grade based on how similar or different the tumor cells look compared to normal tissue
• Tumor grading


  • Low grade tumors look similar to normal tissue, high grade tumors look more different and contain more dividing cells
  • Advantage is it's a low-tech and cheap process, disadvantage is samples can be heterogeneous and grading is somewhat subjective
• Breast cancer grading


  • Grade 1: tissue architecture similar to normal
  • Grade 2: some architectural disorganization, cells look less normal
  • Grade 3: tissue architecture completely chaotic, cells look very immature
• Tumor grade


  Provides important prognostic information and can inform treatment decisions
• Tumor staging


  Process that uses observations from surgery and imaging to characterize the size and spread of a cancer
• Components of tumor staging

  • T (tumor size/invasion)
  • N (lymph node involvement)
  • M (distant metastases)
• Colorectal cancer staging


  • T0: no evidence of primary tumor
  • T1: tumor invades submucosa
  • T2: tumor invades muscularis propria
  • T3: tumor invades through muscularis propria
  • T4: tumor invades visceral peritoneum or other organs
• Colorectal cancer staging


  • N0: no regional lymph node metastasis
  • N1: metastasis in 1-3 regional lymph nodes
  • N2: metastasis in 4 or more regional lymph nodes
  • N3: metastasis to lymph nodes far from primary
• M designation in cancer staging

  Indicates presence or absence of distant metastases
• Tumor stage is determined by combining T, N, and M designations
• Higher stage colorectal cancers have poorer 5-year survival rates
• Imaging modalities


  Techniques used to diagnose and track cancers
• Imaging techniques covered


  • Computerized tomography (CT) scans
  • Magnetic resonance imaging (MRI)
  • Positron emission tomography (PET) scans
• CT scans


  • Detect tumors due to abnormal density or metabolism
  • Use X-rays from multiple angles to create 3D images
  • Involve X-ray exposure but low risk of cancer
• CT scan images


  • 3D rendered brain tumor
  • Slice showing tumor detail
• MRI


  • Detect abnormal density of tumors compared to surrounding tissue
  • Use magnetic fields and radio waves, no radiation exposure
  • Expensive and can be uncomfortable for patients
• PET scans


  • Image tissue function and metabolism, not just density
  • Use radioactive tracers attached to sugars, tumors take up more sugar
  • Can be combined with other imaging techniques
• PET scan images


  • Normal person with some organs lighting up
  • Person with lymph node and bone metastases
• Combining PET and MRI


  Precisely defines the area occupied by a tumor
• Population-wide cancer screening programs

  Designed to detect cancers early in asymptomatic individuals
• Imaging techniques


  Used when people experience symptoms, to figure out what's causing the symptoms and potentially detect cancer
• Population-based screening


  Screening of healthy people in large numbers to identify cancers at an early stage
• Criteria for implementing population-based cancer screening

  • The condition needs to be an important health problem
  • There needs to be a recognizable early stage that can be detected
  • There needs to be an available treatment
  • The test has to be accurate and acceptable to the population
  • There needs to be facilities for follow-up, diagnosis and treatment
  • The cost needs to be balanced with the medical care budget
• Population-based cancer screening programs implemented in Australia

  • Breast cancer screening
  • Bowel cancer screening
  • Cervical cancer screening
• Breast cancer screening


  Uses mammograms (x-rays) to detect unusually dense parts of the breast which may be tumors