S1L1 - Introduction Flashcards
What are the main pathology disciplines?
- Medical microbiology, including virology.
- Immunology.
- Haematology.
- Cellular pathology( histopathology and cytopathology),
- Chemical pathology (clinical biochemistry).
What can histopathology tell us about cancer type?
- Type of cancer
- Stage of cancer.
- Grade of cancer.
- Completeness of excision
- Likely efficacy of further treatments
What steps are used to produce a slide of tissue?
- Fixation
- Cut-up (trimming)
- Dehydration
- Embedding(processing)
- Blocking
- Microtomy
- Staining
- Mounting
- Microscopy
Why do we fix tissue specimens?
To prevent autolysis occurring when blood supply is removed, as this would destroy the cells and tissue architecture.
Fixatives inactivate tissue enzymes and denature proteins, hold tissue is a suspended animation, prevent bacterial growth and harden tissue.
How do we fix tissues?
With formalin. Usually takes 24/48 hours.
What is embedding? why do we do it?
Surrounding and impregnating the tissue specimen with a hardening agent allowing the tissue to be cut into very thin sections.
Usually use paraffin wax.
What must be removed from the tissue specimen before embedding can occur?
Tissue specimen must have water removed as it would not dissolve in the paraffin wax. Dehydrate using alcohol in a vacuum. Replace alcohol with xylene which mixes with wax. Xylene replaced with molten paraffin wax.
What is blocking?
Putting the tissue specimen into metal blocks and filling with paraffin wax, producing a larger solid block of paraffin wax with the tissue specimen preserved inside.
How are tissue specimens cut?
The block is cut using a microtomy, into very thin slices.
What stain is commonly used?
H&E stain
Haemotoxylin - stains nuclei blue. Basic dye
Eosin - stains cytoplasm and connective tissue pink. Acidic dye.
Why mount tissue sides?
Mounting medium applied to the slide with a coverslip on top. This preserves the tissue.
What is immunohistochemistry?
immunohistochemistry demonstrates the presence of substances (usually proteins) in or on cells. Does this by labelling them with specific antibodies. Antibodies joined with an enzyme that catalysed a colour producing reaction. Any antigenic substance can be demonstrated.
What is molecular pathology?
Studies how diseases are caused by alterations in normal cellular molecular biology. Usually refers to changes in DNA (can be RNA, or protein).
Give examples of techniques that are used in molecular pathology
- FISH (fluorescent in situ hybridisation)
- sequencing of DNA purified from tumour
- next generation sequencing
- mRNA expression profiling methods
What are frozen sections and how are they used?
Urgent histological preparations, very quick. Bypass formalin fixation and embedding in paraffin wax. Rapidly freeze small section of tissue on a cryostat, before being thinly sliced stained and mounted.
What is a disease?
A pathological condition of a body part, an organ or a system characterised by an identifiable ground of signs or symptoms.
What is pathology?
Study of suffering. Branch of medicine concerned with disease and understanding the process of disease.
What is neuropathology?
Examination of brain, spinal cord, nerve and muscle cells.
What is forensic pathology?
Medicolegal investigation of suspicious or criminal deaths, attend crime scene, performed detailed autopsies and act as an expert witness in court
What is paediatric pathology?
Tissue samples from children, undertake foetal, perinatal and paediatric autopsies.
What is the importance of microscopic diagnosis?
Gives a definitive diagnosis and guides the type and extent of surgery.
Give examples of when histology is used
Core biopsies, cancer resection specimens, excised skin lesions.
Give examples of when cytology is used?
Fine needle aspirated of breast, thyroid, salivary glands, lung, effusions, cervical smear, sputum, urine.
What are the benefits of using histology?
Often therapeutic as well as diagnostic
Can assess architecture as well as cellular atypia.
Can differentiate invasive from in situ disease.
Can provide information on completeness of excision and more complete information on grading and staging.
Better for immunohistochemical and molecular testing
What are the benefits of cytology?
Faster and cheaper, generally safe
Non-invasive or minimally invasive and safe
Can be used for cells in fluids
Sometimes a preliminary test before other investigations or more tissue taken for histology
Generally used to confirm/exclude cancer/dysplasia
Where do serous carcinomas occur?
Ovary Fallopian tube Uterus Cervix Peritoneum
What can histopathology tell us about cancer?
Type fo cancer Grade of cancer Stage of cancer Completeness of excisions Likely efficacy of further treatments
What 3 factors are considered when staging a cancer?
TNM
T = tumour (size and location)
N= nodes (spread or localised)
M = metastasis ( invasive or not)
How do we prevent autolysis?
Prevent autolysis to prevent cell destruction and tissue architecture by using fixatives. Usually use formalin (formaldehyde in water)
What is the function of tissue fixatives?
To preserve tissue samples by:
- inactivating tissue enzymes and denaturing proteins
- preventing bacterial growth
- hardening tissue
What is the function of paraffin wax?
A hardening agent. Allows tissue samples to be cut very thin and examined under a microscope
After fixation, what must be done to tissue samples before hardening?
Dehydrated. Done by using alcohol in a vacuum to draw water out of cells. Them alcohol is replaced with xylene before being replaced again with molten paraffin wax
What machine is used to cut samples of tissues after it being embedded in a paraffin wax block?
Microtome
What is immunohistochemistry?
Demonstrating substances in/on cells by labelling them with specific antibodies. If the antigenic substance is present there is usually a colour producing reaction with substances highlighted brown.
Give some examples of antigenic substances?
Contractile protein actin Cadherins Hormone receptors HER2 receptors Microorganisms
What are cytokeratins?
A family of intracellular fibrous proteins present in epithelia. Show tissue specific distribution in epithelia and can be used as markers. Give information about the primary site of a carcinoma
What is FISH?
Fluorescence in situ hybridisation. Used to show how DNA has been altered in cells. Used to test for gains of additional copies of HER2 gene in breast cancer.
Why is it helpful to sequence DNA purified from a tumour?
Can see if there is a mutation in a certain gene such as EGFR gene. If a mutation in the EGFR gene is present this indicates the lung cancer is likely to respond to particular treatments such as anti-EGFR treatments.
When are frozen sections used?
When urgent histopathology is needed. Used intra-operatively to influence the course of an operation
What is the advantages of frozen sections?
Quick (10 minutes), intraoperative
Can be used in urgent situations.
Why are frozen sections not routinely used?
Morphology not as good as in paraffin sections
As not as accurate, architecture may be misinterpreted.
can cause false negatives
What can mRNA expression profiling methods show?
How active genes are, at RNA level. This can help predict how a tumour will behave.
What is medical microbiology?
Study of infectious disease causing microbes, give advice on infection control and antibiotic usage.
what is immunology?
Study diseases of the immune system. Allergies, autoimmunity, immunodeficiency.
Why does autolysis occur when a tissue sample is taken?
Release of enzyme from lysosomes inside the cells.
Released enzymes digest the cell, cell bursts and enzymes damage the extracellular tissue
What is the most commonly used fixative?
Formaldehyde in water / formalin
what is haematology?
Study disorders of the blood. Conduct blood transfusions and bone marrow transplants.
what is cellular pathology?
Macroscopic and microscopic assessment of tissue samples and provision of clinically relevant and useful reports. Autopsies. Includes forensic pathology, neuropathology and paediatric pathology.
what is chemical pathology?
Conduct biochemical investigations of diseases. Study disturbance of metabolic processes.
why is microscopic diagnosis of lesions important?
- needed before any major surgical removal - guides necessity and extent
- guides type of treatment required
- gives a definitive diagnosis
what samples are used in histology?
microscopic slides prepared from tissue sections
what samples are used in cytology?
cells scraped from or sucked out of an organ or lesion or extracted from a body fluid such as urine or a pleural effusion
what are the disadvantages of cytology?
Higher inadequate and error rates
used to confirm/exclude cancer/dysplasia but not able to diagnose any other condition with accuracy
what is inflammation?
vasodilation causing inflammation of cells. usually caused in infection
what is a serous carcinoma?
a malignancy of epithelial cells
what considerations must be made when handling cellular samples?
identity of the patient is not lost - we must know who the specimen is from and not mix it up with any other patients.
Tissue is placed in a container to which is affixed a label bearing the patient’s details, usually name, address, date of birth, identification number etc.
These details are also attached to a request form, that must be filled out, giving such details as the clinical summary and provisional diagnosis.
what is immunohistochemistry used for?
identifying smooth muscle - contractile protein actin
used to give information about the primary site of a carcinoma - cytokeratins
foreign microorganisms - CMV, HPV, herpes simplex
hormone receptors - oestrogen receptor, progesterone recepetor
Her2 receptor - a GF receptor that predicts the response of breast cancer to the drug herceptin
