AMC-HC 7: Invasion & Metastasis

Question 1

When are most tumors noticed?

Answer 1

When they start influencing the function of organs and tissues

Question 2

Tumor metastasizing potential differs per tissue. Which cancer has a high risk for metastasis? And which have a lower risk?

Answer 2

Melanomas – high
Basal cell carcinomas of skin and astrocytomas – low

Question 3

Stages of metastases

Answer 3

Intravasation
> Transport through cicrulation
> Arrest in microvessels of various organs
> Extravasation
> Formation micrometastasis
> Formation Macrometastasis

Question 4

For carcinomas, the most common cancers, to invade, they need to break through the basement membrane. Which enzymes help them?

Answer 4

Proteases that cleave the ECM > malignant cells locally invade nearby tissues and gain access to growth factors and blood supply of the stromal niche

Question 5

Which action increases the risk of metastasis enormously?

Answer 5

Breaking through the basement membrane

Question 6

How do macrophages enable intravasation of cancer cells into the circulation?

Answer 6

They secrete EGF > stimulation intravasation

Question 7

Why is the blood a hostile environment for cancer cells?

Answer 7

-No support from stroma cells
-No contact with other cells
-Hydrodynamic shear stress in vessels
-Not built for microcapillaries (they have large nuclei and do not fit well.

Question 8

A readout for risk for metastasis (useful for therapy), is made by measuring …

Answer 8

Circulating tumor cells (CTCs)

Question 9

What is a problem with measuring CTCs?

Answer 9

Complicated comparisons between cancers and patients

Question 10

Detection of tumor DNA

Answer 10

Mutation profile: mutations and translocations

Question 11

Most CTCs spend little time in cicrulation. Where do they end up? and can they escape this place?

Answer 11

They get stuck in the lung microcapillaries > but they can escape and get stuck nearby other organs in the systemic circuit and metastase there.

Question 12

What characteristic of cancer cells is essential for metastasis?

Answer 12

Their size: they have to get stuck in microcapillaries to be able to invade

Question 13

Mechanisms of extravasation by cancer cells

Answer 13

-Through the endothelium
-Growing within the vessel

Question 14

When cancer cells escape from vessels, they enter a new environment with growth factors and new stroma cells et cetera. Does this have a positive or negative effect on the cancer cell?

Answer 14

Can be either positive or negative

Question 15

Colonizing cancer cells first form micrometastases. From which number of micrometastasis, a macrometastase is formed?

Answer 15

There is no vast number > the chance of forming a macrometastasis is very low

Question 16

Why is the chance of formation of micrometastasis very low?

Answer 16

The new environment is not compatible to a single cancer cells most of the times.

Question 17

The incedence of micrometastases has a negative effect on the patients …

Answer 17

prognosis

Question 18

Differences between initial micrometastases and secondary wave

Answer 18

-Initial micrometastases: generically distinct: cells can disseminate but not colonize > different mutagenic profiles (selection, only the best adapted cells will be able to form micrometastases and macro)
-Secondary wave: generically similar, derived from the primary metastasis which was adapted well to the colonization of new tissues.

Question 19

Secondary wave of metastases is also called the …. and is responsible for the …

Answer 19

Metastatic shower > most deaths (faster growth because of better adaptation)

Question 20

Micrometastases will die after a few days if they do not grow, true/false?

Answer 20

False: they can remain dormant for large periods of time > waiting for colonization

Question 21

Which transition enables invasion?

Answer 21

Epithelial-mesenchymal transition (EMT)

Question 22

What do carcinoma cells need to do to acquire motility and invasiveness?

Answer 22

-Shed epithelial phenotypes, detach from epithelial sheets
-Undergo the epithelial–mesenchymal transition (EMT)

Question 23

EMT is also required for normal healthy processes. Name one

Answer 23

Embryogenesis or wound healing response
> Carcinomas can thus activate the latent program which is usually confined to early embryogenesis and to damaged adult tissues!
> the TF’s for EMT induction are relevant

Question 24

EMT involves changing of shape, acquisition of motility and fundamental alterations in gene expression. Name EMT related gene regulations

Answer 24

-Downregulation of E-cadherin and cytokeratins (hallmarks of epithelial cells)
-Upregulation of vimentin (large intermediate filament component of the mesenchymal cell cytoskeleton)
-Twist gene > stimulates EMT: lower expression of epithelial markers E-cadherin, beta-catenin, and gamma-catenin and higher mesenchymal marker expression: fibronectin and vimentin

Question 25

E-cadherin role

Answer 25

Transmembrane protein: the extracellular domain functions as a hook which can links cells with E-cadherin to each other > the intracellular domains are tethered to the actin fibers of the cytoskeleton via an complex of alfa/beta-catenins. The actin cytoskeleton provides tensile strength.

Question 26

Loss of E-cadherin

Answer 26

Beta-catenin goes free into the cytosol and translocates to the nucleus to promote proliferation genes via binding to TF's (Wnt signaling) > also, connectivity between adjacent cells decreases.

Question 27

Which signaling is involved in EMT induction?

Answer 27

Paracrine / autocrine

Question 28

How can tumor associated macrophages promote EMT in cancer cells?

Answer 28

By secreting TNF-alfa or EGF

Question 29

Is EMT a reversible process?

Answer 29

Yes, after colonization, cancer cells can undergo a mesenchymal-epithelial transition (MET)

Question 30

EMT transcription factors can also induce a special state of cells. Which one?

Answer 30

Stem cell state: needed for cancer cells to grow and metastasize. > EMT program can enable carcinoma cells to translocate from the core of primary tumor to foreign tissue during metastasis

Question 31

Why is stemness important for carcinoma cells?

Answer 31

It endows disseminating carcinoma cells to be able to form metastases and to grow.

Question 32

Why are extracellular proteases important for invasion?

Answer 32

Remodeling of nearby tissue > excavating passageways through ECM and breaking the basement membrane

Question 33

Which extracellular proteases excavate the ECM?

Answer 33

Matrix metalloproteinases (MMPs like MMP2) > these proteases are secreted by macrophages, mast cells and fibroblasts.

Question 34

How is the activity of MMPs normally controlled?

Answer 34

By the secretion of inactive pro-enzymes but in cancer, the proteolysis is a continuous process.

Question 35

Which kind of expression of MMPs can drive carcinogenesis?

Answer 35

Ectopic expression of MMPs

Question 36

What is a marker of metastasis?

Answer 36

Cancer cell positive lymph nodes

Question 37

The site of metastasis has a certain risk per type of primary tumor. Which metastases mostly occur with prostate cancer? And with breast cancer?

Answer 37

Prostate: to bone marrow Breast cancer: to lungs and bone marrow

Question 38

What is the affinity of different primary tumors /cancers towards a certain organs for metastasis called?

Answer 38

Tropisms to these organs

Question 39

Why do tropisms exist?

Answer 39

Because cancer cells are uniquely equipped for colonizing different sites (ability to colonize certain organs is rarely achieved)

Question 40

Seed and soil hypothesis

Answer 40

metastizing cancer cells (seeds) find compatible home only in certain hospitable tissues (soil)

Question 41

What is another factor (besides certain cancer being equipped better for metastasis in certain organs) for tropisms (preference for metastasis tissue)?

Answer 41

The layout of vessels and the route of cancer cells through the curculation

Question 42

What sites can attract certain cancer cells?

Answer 42

Sites of chronic inflammation > more blood flow towards the inflammation site > blood flow patterns may explain metastase patterns

Question 43

Tumor self-seeding

Answer 43

Tropism towards the site of the primary tumor

Question 44

Vascular ZIP code (adres) theory

Answer 44

receptors on the walls of capillaries attract circulating tumor cells

Question 45

Prediction of metastase sites:

Answer 45

66% (majority): blood flow patterns 20% specialized microenvironments of target tissues 14% by negative interactions > tissues actively repelling cancer cells

Question 46

Why do micrometastases reduce the long-term survival of patients?

Answer 46

-Dormant micrometastases are often non-cycling and thus resistant to therapy

Question 47

Why do immunosuppressed patients have explosive development of aggresive metastatic disease?

Answer 47

The immune system may suppress the growth of micrometastases

Question 48

What proves the genetic determinants of metastases?

Answer 48

Only a subpopulations of genetic diversity of primary tumor found in metastases, so selection-based