Neoplasia 4

Question 1

PARENCHYMA

Answer 1

Neoplastic population of cells in a tumour

Question 2

STROMA

Answer 2

Non-neoplastic support structure. 
Comprises extracellular connective tissue proteins and glycoproteins embedded in a proteoglycans matrix. 
Blood vessels provide nutrition
Fibroblasts
Inflammatory and immune cells.

Question 3

MESENCHYMAL TUMOURS

Answer 3

eg. sarcomas.
These produce THEIR OWN ECM, from the stroma of the tumour.
eg. an osteosarcoma produces bone.

Question 4

EPITHELIAL TUMOURS

Answer 4

eg. carcinomas.
The SURROUNDING MESENCHYMAL NON-NEOPLASTIC CELLS PRODUCE ECM.
They may also produce a capsule, giving a better prognosis (clear margin for excision)

Tumours can also produce ‘bizarre things’- eg. plasmacytomas can produce amyloid.

Question 5

TUMOUR-STROMAL INTERACTIONS

Answer 5

Interactions are complex- 2 way between tumour and stroma.
They become interdependent on one another.
A wide variety of signalling molecules are involved- cytokines, growth factors, hormones (in endocrine tumours), inflammatory mediators.
-These modulate growth rate, differentiation state and behavious of BOTH cell groups.
eg. Tumour release of PDGF
eg, Tumour derived TGFa (Transdforming Growth Factor a) causes fibroblasts to differentiate to myofibroblasts and pericytes to move to edges of vessels, allowing angiogenesis to occur.

Question 6

eg. ADENOCARCINOMA IN THE EYE

Answer 6

Tumour cells release Platelet Derived Growth Factor.
This activates tumour associated fibroblasts.
There is increased collagen production- scirrhous/dermoplastic response from non-neoplastic mesenchymal cells.

Question 7

INFLAMMATION

Answer 7

Often heavy infiltrates of neutrophils, eosinophils, Mast cells, lymphocytes and histiocytes.
Attracted by chemokines and cytokines.
eg. Lymphocyte infiltration often seen in FISS (Feline Injection Site Sarcoma)

INFLAMMATION IS NOT NECESSARILY PROTECTIVE.
eg. Studies suggest that NSAIDs reduce tumour incidence (NSAID = reduced inflammation = reduced tumours?)

Question 8

TUMOUR IMMUNITY

Answer 8

1. Tumour antigens
2. Immunosurveillance
3. Antitumour effector mechanisms- NK cells, macrophages, T cells, B cells.
4. Evasion of immune response.
5. Tumour immunotherapy.

Question 9

TUMOUR ANTIGENS

Answer 9

Surface expressed proteins/glycoproteins/glycolipids or carbohydrates.
Can be tumour specific (most useful) or tumour associated.

CLINICAL APPLICATIONS:

• Diagnostic tool
• Therapeutic tool- Monitoring response to therapy
  - Complex imaging using antibodies against tumour restricted antigens- can be used to localise tumours and find metastases.

Question 10

TUMOUR SPECIFIC ANTIGENS

Answer 10

Often newly expressed:

• Oncogenic viruses
• Altered cellular products (mutated genes)
• Embryonic or oncofoetal antigens can be produced by reexpression of embryonic/oncofoetal genes.
  eg. Carcinoembryonic antigen, a-fetoprotein.

Question 11

TUMOUR SPECIFIC SHARED ANTIGENS

Answer 11

Expressed by MANY tumours, seen in limited numbers of normal adult tissues.

eg. MAGE family of proteins
- Promising possibility for antitumour immunotherapy.

Question 12

TISSUE SPECIFIC ANTIGENS

Answer 12

Shared by tumours and normal tissues.
eg. Differentiation antigens (expressed at a SPECIFIC differentiation stage in normal tissues)

These antigens are useful if they are expressed at a higher level on tumour cells than normal cells.
This makes them function like tumour specific antigens.

Question 13

IMMUNOSURVEILLANCE

Answer 13

-Suppresses tumour development by recognising self antigens on tumour cells as ‘foreign’.
Immune system then attacks as if infected with microbes.

Failure of immunosurveillance causes tumours to emerge.
The strongest evidence for this is the susceptibility of immunocompromised transplant patients to tumours.

Question 14

IMMUNOHISTOCHEMISTRY

Answer 14

Used after H&E and special stains to DETECT SPECIFIC ANTIGENS.

DIRECT: Enzyme labelled primary antibody reacts with tissue antigen.

INDIRECT: Enzyme labelled secondary antibody reacts with primary antibody bound to tissue antigen.

Positive = BROWN.
eg. CD3 marker is used to detect T cells.

Question 15

ANTITUMOUR EFFECTOR MECHANISMS

Answer 15

Dependent on immune responsiveness of host and on characteristics of tumour antigen.

INNATE IMMUNE SYSTEM- First line of non specific attack.
NK cells, macrophages.
NO dendritic cell priming is required.

ADAPTIVE IMMUNE SYSTEM- Cell mediated and humoral branches.
Antigens must be presented in a recognisable form- dendritic cells play a CENTRAL role.

Question 16

NATURAL KILLER CELLS

Answer 16

NK cells. Part of innate immune system. 
LYMPHOCYTES- bone marrow derived
-Lack usual B and T cell markers
-Kill neoplastic and virally infected cells. 
-Specifically target MHC FREE cells. 

When the NK cell contacts tumour, it releases lytic granules, causing apoptosis (cytolysis) of target cells.

Question 17

MACROPHAGES

Answer 17

No priming required, but do require direct contact.
T cells and NK cells release IFNy (interferon gamma), which STIMULATES circulating macrophages to release:
-ROIs
-LYSOSYMAL ENZYMES
-NITRIC OXIDE
-TNFa

-> cytolysis and death of tumour cells.

Direct contact!!!

Question 18

CYTOTOXIC T LYMPHOCYTES

Answer 18

Adaptive immune system.
CD8.
Primary effectors of adaptive anti tumour immune response.
-Primed by dendritic cells to recognise TUMOUR ANTIGENS on cells surface.
-Stimulate apoptosis.

Do not react to normal host cells displaying MHC associated self antigens.
DO react to their specific tumour antigen, displayed specifically on the tumour cell.
This activates the T cell.

Question 19

MAIN 4 TUMOUR ANTIGENS

Answer 19

1. Oncogene/mutated suppressor gene
2. Mutated self protein
3. Over or aberrantly expressed self protein
4. Oncogenic virus.

Question 20

CYTOTOXIC T CELLS contd.

Answer 20

Attach to target cell
-> Immunologic synapse forms
-> Lytic granules released:
PERFORINS- Pore forming, mediate entry in to target cell.
GRANZYMES- Serine proteases, initiate apoptosis.

Question 21

DENDRITIC CELLS

Answer 21

Fragment antigens and present them on their surface in such a fashion that allows activation of T and B cells.
Dendritic cells play a central role in the ADAPTIVE immune response.

T cells and B cells can then go on to lyse cells or produce antibodies respectively.

Question 22

B LYMPHOCYTES

Answer 22

Adaptive immune system.
Produce antibodies and mediate the HUMORAL response to tumours:

ANTIBODIES recognise tumour antigens

• > activate local complement cascade
• > generate a Membrane Attack Complex
• > tumour cell membrane damaged
• > rapid cell death by NECROSIS.

Question 23

HELPER T LYMPHOCYTES

Answer 23

Part of adaptive immune system.
CD4.
Enhance CD8 (cytotoxic T cells) and B cell function.

Question 24

IMMUNE EVASION BY TUMOURS

Answer 24

1. Failure to produce tumour antigen.
   An antigen loss variant of tumour cells is favoured by clonal expansion, or antigen is hidden by fibrin or antibodies.
2. Mutations in MHC genes or antigen processing genes.
   eg. Class I MHC-deficient tumour cell.
3. Production of immunosuppressive T cells (eg. cytokines- damage T cells)
4. Tolerance- Tolerant to self antigens (eg. those shared with normal tissue)
   - Presentation of non-self antigens without co stimulatory molecules.
5. Immunosuppression- Tumour cells or products may be immunosuppressive.
   eg. Fas ligand- binds to Fas receptors on T lymphocytes and triggers their apoptosis.
   - Tumour cells release antigens into circulation, where they form immune complexes which may be immunosuppressive.

Question 25

TUMOUR IMMUNOTHERAPY

Answer 25

Effective immunotherapy is preferable to cytotoxic chemotherapy, which is indiscriminate and targets dividing cells.

STRATEGIES:
Provide mature effector cells to recognise and destroy tumours. This is PASSIVE immunotherapy.

ACTIVE immunotherapy- stimulates host immune response against tumour.
Coupling toxins to monoclonal antibodies may allow targeted delivery of therapeutic agents to tumour cells.

Question 26

TUMOURS: DIRECT SYSTEMIC EFFECTS ON HOST

Answer 26

Replace normal tissue, so affect function.

• Space occupying effect
• Erosion of vessels can cause acute haemorrhage
• Emboli passing in to vessels may cause infarcts at a distant site (common in kidneys and spleen, less so in lungs due to collateral circulation)
• Blockage of vessels eg. Lipoma strangulation colic in horses.

eg. Choroid plexus hyperplasia- can be benign, but this still has space occupying effects.
This has direct effects:
-Astrocytes cause scarring.
-Gitter cells remove myelin.