Paul Lawrence-Young

• Fixation in histopathology attempts to preserve the tissues in a life-like condition by preventing autolysis and putrefaction.
• Areas of interest, clearance margins, depth of invasion, and pleomorphic tumour are all aspects of a specimen that need to be considered during dissection.
• Representative samples in histopathology can include UOQ, UIQ, LUQ, LIQ, tumour, nipple, lymph nodes.
• Additional testing can include molecular testing for targeted drug therapy, for example, ALK-1 +ve indicates Permatrexed for adenocarcinoma, EGFR +ve indicates Gefitinib, Erlotinib & Afatinib, and PDL-1 in squamous cell carcinoma.
• Frozen section in cytology allows for very rapid differentiation between malignant and non malignant.
• Embedding in microtomy involves orienting the tissue, cutting the edge must be flat, and requires a VERY gentle touch.
• Special stains for micro-organisms include Gram stain, Ziehl-Neelson stain, and Grocott stain.
• Special stains for morphology include reticulin, collagen, glucose +ve, and CAP/Hepatitis.
• Formalin fixed tissue, graded industrial methylated spirit, xylene, and molten paraffin wax are all used in the histopathology processing stage.
• Formalin is made out of Formaldehyde and saline in a buffer
• Benign tumors are different to malignant ones in which they are non-cancerous growths or masses of cells that do not have the ability to invade surround tissue or spread to other parts of the body.
• Cancer cells are different to normal cells in which they:

  - Grow in absence of signals telling them to grow

  - Ignore signals that tell cells to stop dividing or to die ( ignore apoptosis and cell programmed death)

  - Invade nearby areas

  - Tell blood vessels to grow towards tumors

  - Hide from the immune system
• Samples like a tiny biopsy of skin you will want to sample it using a punch biopsy. A punch biopsy is a medical procedure commonly used to obtain a small sample from the body for diagnostic purposes this technique is commonly used to investigate skin lesions.
• When handling biopsies and samples that have been received in histology we must follow 3 steps:

  1. Preserve

  2. Select

  3. Identify
• Formalin works by cross-linking proteins. Formaldehyde reacts with amino groups in proteins and forms covalent cross links between adjacent proteins which therefore stabilises protein structure and prevents further degradation. By cross linking we destroy the active site and the enzymes used for autolysis can not work.
• Factors affecting fixation:

  - Time

  - Volume ratio of formalin

  - Type of tissue

  - Temperature

  - Tissue size and thickness
• Select the areas of interest – find out which area is affected and work around that area
• Clearance margins- making sure that the surgeon removes the tumor and take out a surrounding area of healthy tissue so no cancer cells are left behind.
• Depth of invasion- the extent to which cancer cells have invaded surrounding tissues
• - Pleomorphic tumor- more and more different mutations
• Oil and water do not mix… how do we preserve? Slice the sample not all the way through stop at the skin layer and this increases the SA:V. To counter this problem: 1. Ink the margin 2. Slice laterally 3. Wick the tissue 4. Further fixation for minimum 24hrs 5. Consultant dissection.
• The alcohol replaces the water Xylene replaces alcohol xylene is an organic solvent which mixes with paraffin therefore you get that candle.

• Benign tumors have a more localised and contained growth in comparison to malignant ones although benign tumors may cause health issues depending on size and location they do not pose the same threat to life like malignant ones.