W8 Invasion and Metastasis (GN)

Question 1

What is Metastasis?

Answer 1

=Spread of cancer cells from a primary tumour to a distant site within the body to establish a secondary tumoral growth

Cancer hallmark → (metastasis is) only in malignant tumours

• Metastasis is responsible for 90% of the deaths in patients with cancer
• Important prognostic value (associated with poor prognosis)
  o Impairing organ functionality
  o Difficult to eradicate surgically
  o Usually chemo-resistant

Question 2

Metastasis - what are the routes of spread? (4)

Answer 2

1. Lymphatic system- Spread first to the closest regional lymph nodes (sentinel lymph node) and then to other parts, following natural route of drainage
2. Circulatory system (hematogenous spread)- Because of thinner walls, capillaries are the favoured routes, then
   following the pattern of cardiovascular flow. (most common route)
3. Transcoelomic (body cavities)- Spread by penetrating the surface of the body cavities (e.g. peritoneal, pleural, pericardial)
4. Canalicular spread- Spread along anatomical canalicular spaces( e.g. the bile ducts, the urinary system)

Question 3

The Anatomic Model vs “Seed and Soil” Hypothesis:
What are the 2 theories?

Answer 3

➢Anatomic theory
* Follow the blood/lymphatic flow
* Secondary tumours tend to occur in organs which are first encountered by the disseminating cancer cells
* the size and shape of capillaries influence cell arrest

➢“Seed and soil” theory
* metastases resulted only when the appropriate seed (primary tumour) was
implanted in its suitable soil (metastasis site)
* Microenvironment (growth factors and extracellular matrix stroma composition)
plays a critical role in supporting the successful colonisation of metastases

Question 4

Metastasis development steps
What are the 5 major steps?

Answer 4

1) Tissue Invasion
2) Intravasation
3) Circulation & Survival
4) Extravasation
5) Colonisation

Question 5

Cancer invasion
What is Local invasion?

Answer 5

• Events involving the detachment of cancer cells from a well-confined primary
  tumour and their consequent infiltration and invasion of the surrounding tissue

Question 6

Local invasion
Loss of cell-cell interaction
In normal cells:

Answer 6

• Epithelial cells adheres to adjacent
  cells and the extracellular matrix
  through cell junctions
• Cell junctions are mainly mediated by E-cadherins
• E-cadherins are linked intracellularly to β-
  catenin of the cytoskeleton

Question 7

Local invasion
Loss of cell-cell interaction
In tumoral cells:

Answer 7

• Altered E-cadherin (or β-catenin) expression leads to weak cell-cell adhesion
• Altered expression of integrins
  ▪ trans-membrane proteins provide interactions with components in the extracellular matrix
  ▪ establishing traction for cellular motility and invasion
• These alterations make the cells free and contribute to cell mobility and invasiveness

Question 8

Local invasion

Answer 8

• Expression of Matrix Metalloproteinases (MMPs) to disassembly the basement membrane and extracellular matrix→ creating a path to facilitate invasion
• MMPs are elevated in most cancer types → poor prognosis

Matrix degradation
Cancer cells

Cell motility
* Cytoskeletal changes → altering cell morphology and
forming cell protrusions (pseudopodia)
* Actin/myosin contractile forces drives cell motility
* Chemotaxis → growth factors guide cell movements

Question 9

Epithelial-Mesenchymal Transition for invasion (summary):

Answer 9

Epithelial state:
* Defined Cell polarisation/shape
* Firm cell-cell adhesion
* No migratory/invasion potential
* Expressing E-cadherins

Mesenchymal state:
* Loss of cell polarisation/shape
* Loss of cell-cell adhesion
* Ability to migrate and invade
* Low level of E-cadherins

Question 10

Angiogenesis:
What is it?
What is it a hallmark of, thus facilitating what?

Answer 10

Formation of new blood vessels from pre-existing vascular beds.

It is a cancer hallmark
- Essential to provide nutrients &
oxygen and remove metabolic wastes
It is needed to further grow tumoral
masses (>2mm)
- Facilitates metastasis

Question 11

Angiogenesis switch in tumours
Is there angiogenesis in normal cells, when? (important)

Answer 11

In normal cells:
* Normally, angiogenesis is inhibited
* Or induced in wound healing or menstruation
(more anti-angiogenic factors)

In tumoral cells:
* Hypoxia & mutations stimulates cancer
cells to overexpress pro-angiogenic
factors (VEGF, PDGF, TNF-α, etc)
* VEGF induces the proliferation of
endothelial cells of blood vessels
VEGF is the target of Avastin (antibody
binding VEGF) to block angiogenesis
(more Pro-angiogenic factors (VEGF))

Question 12

Angiogenesis steps: (no need to memorise)

Answer 12

1. Resting endothelial cells, dormant tumour
2. Endothelial cell activation and production of proteases
3. Endothelial cell migration and start of sprouting
4. Endothelial cell proliferation and sprout formation
5. Endothelial cell maturation

Question 13

Normal vs tumoral vasculature (extra material)

Answer 13

• Tumour vasculature is abnormal
  (irregular, tangled, leaky) → leading to
  hypoxic areas
• Due to an excess of pro-angiogenic
  factors

▪ Uneven chemotherapy drug delivery → suboptimal dosage →potential drug resistance

Question 14

Intravasation, Circulation & Survival, Extravasation

Answer 14

2) Intravasation
* Cancer cells must attach, degrade the basement membrane and migrate between
endothelial cells to enter the bloodstream (or lymphatic system)

3) Circulation & Survival
* Single cells or aggregates (emboli) travel with the blood/lymph flow (hostile environment)
* Cells must avoid immune destruction and their movement is arrested at target sites

4) Extravasation
* Cell attachment to the endothelial lining and passage between cells
* Destruction of the basement membrane and cell escape into the surrounding stroma

5) Invasion and Micro-metastasis
* Cancer cells invade and replicates in the tissue and form small clumps/colonies
* MET Differentiation - from mesenchymal to epithelial cells (inverse of EMT)
* Angiogenesis is required to grow further or cancer cells could undergo dormancy

Colonisation
* Cell growth from micro-metastasis into macroscopic tumours (low success rate)

Question 15

Cancer Staging
What does a tumour stage describe?
What are the Two types of cancer staging systems?

Answer 15

• Tumour STAGE describes the extent of the tumour growth and how far it has spread within the body:
  ▪ estimating a person’s chance of recovery or survival (prognostic factor)
  ▪ helpful to plan the appropriate treatment
  ▪ compare and standardise treatment results between clinical/research studies

➢TNM system
➢Number system

Question 16

TNM - Staging System:
What are the 3 letters involved and what do they represent?

Answer 16

T= Tumor size (0-4)
N= Lymph nodes spread (0-3)
M= Metastasis spread (0-1)

T:
* TX: Tumor cannot be evaluated
* T0: No evidence of tumor
* Tis: Carcinoma in situ
* T1-T4: Size/extent of tumor

N:
* NX: Lymph nodes cannot be evaluated
* N0: No lymph node involvement
* N1-N3: Increasing degree of regional
lymph node involvement

M:
*MX: Metastasis cannot be evaluated
* M0: No metastasis
* M1: Metastasis is present

E.g. → a cancer with a T4 N3 M1 stage is more advanced than a cancer with a T2 N1 M0 stage

Question 17

Number - Staging System
How many stages?
What do they mean?

Answer 17

Stage 0: Carcinoma in situ (Precancerous State)
Stage I, II, III- Higher numbers mean the disease is more extensive, such as larger tumor size and/or lymph nodes spread
Stage IV- Spread to distant tissues/organs

Question 18

Tumour grading
What does it describe?
what does a low vs high grade mean?

Answer 18

• Tumour GRADE describes a tumour in terms of how abnormal the tumour tissue appears under a microscope when compared to normal cells. Based on:
  ▪ Level of cell differentiation → dysplasia
  ▪ Rate of cell growth

➢ low grade → cancer cells closely resemble
normal cells and exhibit slow growth.
▪ Better prognosis

➢ high grade → cancer cells are poorly
differentiated or undifferentiated and tend to grow rapidly.
▪ Worse prognosis

Question 19

Which of the following best describes the seed and soil hypothesis of metastasis tropism?
Metastatic sites must offer a suitable microenvironment fo

Answer 19

=C

Question 20

What is the key process involved in extravasation

Question 21

Summary

Answer 21

• Metastasis consists of the spread of a primary tumour to a distant site within the body to establish a secondary tumoral growth. It is associated to a poor prognosis
• Metastasis can occur via blood vessels, lymphatics or movement within the body cavities
• Metastasis occurs through multi-step process requiring the disruption of local cell–cell interactions, invasion, penetration of blood or lymphatic vessels (intravasation), escape from those vessels (extravasation), migration and growth.
• Angiogenesis is the formation of new blood vessels from existing vascular beds and increases the chance of cancer metastasis
• Cancer grade assesses the appearance and differentiation of cancer cells, while cancer stage describes the extent and progression of the disease within the body.
• Both cancer grade and stage are crucial for determining the most suitable treatment options and predicting a patient’s outlook.