Week 11: Cellular pathology

• Sample Types and Their Importance

  • Small Tissue Samples
  • Medium Tissue Samples
  • Large Tissue Samples
  • Cytological Samples
• Small Tissue Samples

  • Endoscopic Samples: Obtained from colon, esophagus, and bronchial tubes; essential for diagnosing diseases accessible via luminal surfaces
  • Needle Biopsy: Used for organs like liver, lung, breast, and prostate; crucial for diagnosing solid tumors
  • Scrapes/Curettings: Involves mechanical removal of epithelium, such as skin or endometrial curettings, typically for surface lesions
• Medium Tissue Samples

  • Incisional Biopsy: A diagnostic approach involving the removal of a small portion of tissue including the lesion and some normal tissue to determine the nature of the abnormality
  • Excisional Biopsy: Curative procedure where the entire lesion or affected organ is removed with a margin of healthy tissue to ensure no residual disease
• Large Tissue Samples

  • These can include whole organs or large resections, both benign and malignant, and are critical for removing diseased tissue completely to prevent the spread of conditions like cancer
• Immunohistochemistry (IHC)


  • Technique: Involves the layering of specific antibodies to detect proteins or antigens within tissues, used for both diagnostic and prognostic purposes
  • Applications: Identifies markers such as ER and PR in breast cancer, which can predict response to treatments like Tamoxifen or Herceptin
• Immunofluorescence (IMF)


  • Direct IMF: Used for diagnosing conditions like pemphigus or renal diseases by detecting immune deposits in tissues
  • Indirect IMF: Utilizes patient serum to detect auto-antibodies against specific tissue antigens, critical in diagnosing autoimmune diseases
• Fluorescence In Situ Hybridisation (FISH)


  • Application: Particularly useful in oncology for identifying chromosomal abnormalities in cancer cells, such as HER2 gene amplification in breast cancer, which determines the suitability of specific therapies
• Polymerase Chain Reaction (PCR)


  • Utility: Amplifies DNA to detect very low levels of genetic material, useful in identifying pathogens, cancer markers, or genetic mutations from minute samples
• 1. Fixation: Stops cellular breakdown and preserves tissue architecture. Formalin is most commonly used due to its effectiveness in preserving cellular details
• 2. Processing: To replace tissue water with wax, providing stability for thin sectioning. Tissue samples undergo a sequence from formalin to alcohol (IMS), xylene, and then to wax
• 3. Embedding and Sectioning:

  
  

  Embedding - Tissue is oriented in wax within a cassette to ensure proper alignment for slicing.

  
  

  Sectioning - Achieved using a microtome to cut thin tissue sections (2-4 µm thick) that allow for light transmission during microscopy
• 4. Staining:

  Routine Staining (H&E) - Haematoxylin binds to acidic components of the nucleus, and eosin stains basic cellular structures, providing a contrast essential for distinguishing cellular components under a microscope.

  
  

  Special Stains and IHC - Used when routine stains do not provide enough detail.

  IHC employs antibodies tagged with dyes to highlight specific cellular antigens, aiding in detailed diagnosis and prognostic evaluations
• Histopathology Sample Handling Steps:

  1. Fixation

  2. Processing

  3. Embedding and Sectioning

  4. Staining

  5. Sectioning

  6. Staining