S8) Invasion, Metastasis and Effects of Neoplasms Flashcards
Explain why invasion and metastasis are the most lethal features of a malignant neoplasm
- The ability of malignant cells to invade and spread to distant sites leads to a greatly increased tumour burden
- Untreated, this results in vast numbers of “parasitic” malignant cells
Invasion and metastasis is a multi-step journey.
In three steps, explain what is necessary for malignant cells to get from a primary site to a secondary site?
⇒ Grow and invade at the primary site
⇒ Enter a transport system and lodge at a secondary site
⇒ Grow at the secondary site to form a new tumour (colonisation)
At all points the cells must evade destruction by immune cells
Invasion involves three important alterations.
What are they and what effect do they have?
- Invasion into surrounding tissue by carcinoma cells requires altered adhesion, stromal proteolysis and motility
- These changes create a carcinoma cell phenotype that appears more like a mesenchymal cell than an epithelial cell, hence this is called epithelial-to-mesenchymal transition (EMT)
Describe the changes which drive altered adhesion in the process of invasion for malignant cells
- Altered adhesion between malignant cells involves a reduction in E-cadherin expression
- Altered adhesion between malignant cells and stromal proteins involves changes in integrin expression
Describe the changes which drive proteolysis in the process of invasion for malignant cells
- The cells must degrade basement membrane and stroma to invade
- This involves altered expression of proteases, notably matrix metalloproteinases (MMPs)
Explain the role and components of a cancer niche in the invasion of malignant cells
- Malignant cells take advantage of nearby non-neoplastic cells, which together form a cancer niche
- These normal cells provide some growth factors and proteases
Describe the changes which drive altered motility in the process of invasion for malignant cells
- Altered motility involves changes in the actin cytoskeleton
- Signalling through integrins is important and occurs via small G proteins such as members of Rho family
Transport to distant sites is via three routes, what are they?
Malignant cells can enter:
- Blood vessels via capillaries and venules
- Lymphatic vessels
- Coelomic spaces (transcoelemic spread – fluid in pleura, peritoneum, pericardium and brain ventricles)
Explain how malignant cells must grow at a secondary site to form a clinical metastasis and the consequences of this
- Colonisation is when malignant cells successfully grow at a secondary site
- Failed colonisation occurs with many malignant cells which lodge at secondary sites but die/fail to grow into clinically detectable tumours (greatest barrier to successful metastasis)
What are micrometastases?
Micometastases are surviving microscopic deposits which failed to grow at a secondary site
What is the significance of micrometastes?
- An apparently disease-free person may harbour many micrometastases aka tumour dormancy
- When a malignant neoplasm relapses years after an apparent cure it is typically due to one or more micrometastases starting to grow
What determines the site of a secondary tumour?
- Regional drainage of blood, lymph or coelomic fluid
- The “seed and soil” phenomenon
Explain how the regional drainage of blood, lymph or coelomic fluid determines the site of the secondary tumour
- Lymphatic metastasis → regional lymph nodes
- Transcoelomic spread → other areas in the coelomic space / adjacent organs
- Blood-borne metastasis → next capillary bed that the cells encounter (lungs/liver)
Explain how the “seed and soil” phenomenon determines the site of the secondary tumour
The “seed and soil” phenomenon states that the seemingly unpredictable distribution of blood-borne metastases is due to interactions between malignant cells and the local tumour environment, i.e. the niche at the secondary site
How do carcinomas and sarcomas spread?
- Carcinomas typically spread via lymphatic metastasis first and then to blood-borne distant sites
- Sarcomas tend to spread via blood-borne metastasis