1. Introduction to Pathology Flashcards
What is disease?
- A pathological condition of a body part, an organ, or a system characterised by an identifiable group of signs or symptoms
- Disease can be considered to be a consequence of failed homeostasis with consequent morphological and function disturbances
- These disturbances can be manifest at the level of the whole person, an organ, or a tissue. However, in all physical diseases, the cell is the central player.
What is pathology?
- Study of suffering (pathos = suffering, logos = study)
- Branch of medicine concerned with disease and understanding the process of disease
- Attempts to explain why patients experience symptoms and guides treatment
- Often involves diagnosis
what are The main branches of pathology?
• Medical Microbiology which includes: o Virology • Chemical Pathology (Clinical Biochemistry) • Haematology • Immunology • Cellular Pathology (histopathology and cytopathology) which includes: o Neuropathology o Forensic Pathology o Paediatric Pathology
Explain chemical, haem, immuno and micro pathology discipline
Chemical- – Biochemical investigations of disease, e.g., endocrinology, diabetes, lipidology, thyroid disease, inborn errors of metabolism
Haematology- diseases of the blood( clotting, transduction and bone marrow transplantation)
Immunology- disease of the immune system e.g., allergy,
autoimmunity and immunodeficiency
Medical microbiology- disease causing microbes including advice on antibiotic usage
What is the cellular discipline of pathology
histopathology/ cytopathology
– Examine organs, tissues and cells for diagnosis and to guide treatment, often cancer work
– Conduct autopsies
Describe the 4 branches of cellular pathology
- Cytopathology – disaggregated cells rather than tissue
- Neuropathology – confined to brain, spinal cord, nerves and muscle
- Forensic Pathology - medicolegal investigation of suspicious or criminal deaths, attend crime scenes, perform detailed autopsies and act as expert witnesses in court
- Paediatric Pathology – tissue samples from children, undertake foetal, perinatal and paediatric autopsies
What is the importance of a microscopic diagnosis?
• Definitive diagnosis
• Before major surgery to remove a lesion a microscopic diagnosis is required
– This guides the type and extent of surgery
Compare histology and cytology
Histology involves looking at tissue whilst cytology involves looking at specific cells.
H:
• 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
c:
• Faster and cheaper
• 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
• Higher inadequate and error rates
• Generally used to confirm/exclude cancer/dysplasia and not to diagnose any other condition with accuracy
Give examples of histology
Core biopsies, cancer resection specimens, excised skin lesions, endoscopic biopsies
give examples of cytology
Fine needle aspirates of breast, thyroid, salivary glands, lung; effusions; cervical smears; sputum; urine
How does a histopathologist arrive at a diagnosis?
• Pattern recognition
• This histopathologist asks her/himself:
- Is this normal or not?
- Is this inflammatory or neoplastic?
- Is this benign or malignant?
- Is this a primary tumour or a metastasis?`
When a cancer has been identified what further information can a histopathologist tell us?
• Type of cancer
• Grade of cancer ( how ageresive the cancer will be)
• Stage of cancer (what further management is needed)
• Completeness of excision and if margins are involved,
which ones
• Likely efficacy of further treatments (molecular
pathology HER2, ER/PR, EGFR, PDL1 status) (whether certain drug treatments will be effective)
where can serous carcinomas occur?
- Ovary
- Fallopian tube
- Uterus
- Cervix
- Peritoneum
What is the TNM staging system?
It’s a system used to describe the amount and spread of cancer in a patient’s body, using TNM.
- T describes the size of the tumor and any spread of cancer into nearby tissue.
- N describes spread of cancer to nearby lymph nodes.
- M describes metastasis (spread of cancer to other parts of the body).
List the stages involved in tissue sample preparation
- Fixation
- Cut-up (trimming)
- Dehydration
- Embedding (processing)
- Blocking
- Microtomy
- Staining
- Mounting
- Microscopy
- Report writing
What is fixation
- Hold tissue in ‘suspended animation’
- Usually use formalin (formaldehyde in water)
- Penetrates tissue at approximately 1mm/hr
- Usually fix for 24-48 hours
What is autolysis and how do you overcome it?
It is self digestion which begins when the blood supply is cut off, it destroys the cells and tissue architecture
Block this via fixatives(inactive tissues, prevent bacterial growth, harden tissue)
Describe what happens during trimming
• Samples are taken and placed into a cassette
– About the size of a stamp so they can be adequately infiltrated by chemicals
– May need to take 30 or more in complicated cases
– Cassettes have holes in
– They are placed in racks in formalin
Describe what happens during dehydration
This process is used to remove water from tissue.
It involves using alcohol in a vacuum so that water is drawn out of the cells.
The alcohol is then replaced with xylene which can mix with wax.
Describe what happens during embedding
- Molten parafffin wax is used for embedding.
- Tissue is taken out of the cassettes by hand and put into metal blocks.
- These are filled with molten paraffin wax and the body of the cassette is placed on top
- The wax is liquid when hot but dries rock hard when cool.
- The wax is allowed to harden and the metal tray is removed
- This process occurs overnight.
Describe what happens during microtomy
- Very thin (3-4 microns) sections are cut from the block using a microtome
- Sections must be so thin that we can see through them with a microscope
- The thin wax sections are floated on a waterbath and picked up on a microscope slide
Describe what happens during staining
- Colouring of the tissue specimen occurs so it can be seen under a microscope.
- H&E is often used.
- Haematoxylin stains nuclei purple.
- Eosin stains cytoplasm and connective tissue pink.
Describe what happens during mounting
• Mounting medium is applied to the slide
• The coverslip is put on top
• The mounting medium dries and hardens, preserving
the tissue and attaching the coverslip.
Describe what happens during microscopy
The tissue sample is observed under a microscope.
How can immunohistochemistry be used to study tissue
• Demonstrates substances in/on cells by labelling them with specific antibodies
• Usually the antibody is joined to an enzyme (e.g., peroxidase) that catalyses a colourproducing reaction
• Highlights the substances usually with a brown colour
• Any substance that is antigenic can be demonstrated:
– Contractile protein actin – identifies smooth
muscle cells
– Cadherins
– Hormone receptors, e.g., ER, PR
– Her2 receptor
– Microorganisms, e.g., CMV, HPV, herpes simplex
How can cytokeratins be used to provide information about cancer sites
• Cytokeratins are a family of around 20 intracellular fibrous proteins which are present in almost all epithelia.
• Their presence demonstrates epithelial differentiation and the different cytokeratins show tissue-specific distribution.
• They can therefore be used to give information about the primary site of a carcinoma, particularly when used in combination, e.g.:
o CK7+/CK20- : indicates lung, breast, endometrium, ovary or thyroid carcinomas
o CK7-/CK20+ : indicates large bowel or some gastric carcinomas
What is the HER2 receptor?
It’s a growth factor receptor which predicts the response
of breast cancer to the drug Herceptin).
What is molecular pathology?
Molecular pathology is the study of how diseases are caused by alterations in normal cellular molecular biology.
This can be due to altered DNA, RNA or protein, but most often molecular pathology refers to changes in DNA.
What do in situ molecular tests show? Give an example
In situ molecular tests show how DNA is altered in the context of the microscopic tissue structure.
Examples include fluorescence in situ hybridisation (FISH) which tests for gains of additional copies of genes, such as HER2 in breast cancer, which, as with immunohistochemistry for the Her2 receptor, show if a particular tumour is likely to respond to anti-HER2 treatments like Herceptin. FISH tests can also show if genes have been translocated (i.e., broken and/or rearranged) or completely deleted from the genome, and if particular types of viral DNA are present.
What can sequencing of DNA purified from tumour tissue show?
sequencing of DNA purified from tumour tissue can show if a particular point mutation (i.e., a single nucleotide change) is present in a particular gene. This is also very useful; for example, certain mutations in the EGFR gene regularly occur in lung cancers, and again these show that the case is likely to respond to anti-EGFR treatments like erlotinib.
What can mRNA expression profiling methods show?
mRNA expression profiling methods can show how active a large number of genes are, at the RNA level. This is also useful diagnostically, as mRNA expression ‘signatures’ can predict how a given tumour is likely to behave, e.g., the risk of cancer spread/recurrence after surgery for breast cancer.
What is a frozen section?
Frozen sections are histological preparations that, in view of time constraints, bypass the processes of formalin fixation and embedding in paraffin wax and instead involve rapidly freezing a small piece of fresh tissue on a cryostat.
This piece of tissue can then be sliced thinly, stained, mounted and passed to a pathologist for microscopy. The whole process takes about 10 minutes from receipt of the tissue in the laboratory to provision of a result to a clinician.
When are frozen section used?
Tissue for frozen section is taken during the course of an operation with the aim of establishing the presence and nature of a lesion whilst the patient is still under anaesthetic.
Compare the quality of a frozen section to that of a routine paraffin wax embedded section
Frozen sections are harder to interpret than routine paraffin wax embedded sections as the cell morphology is less well preserved and not as easy to interpret. For this reason, errors, usually false negatives, can occur with frozen sections.
