The document summarizes the process of cancer metastasis through the invasion-metastasis cascade. It involves 6 key steps: 1) Localized invasion of primary tumor cells aided by loss of cell adhesion molecules and matrix metalloproteinases. 2) Intravasation of tumor cells into blood vessels assisted by tumor-associated macrophages. 3) Transport of circulating tumor cells protected by platelet emboli. 4) Extravasation of tumor cells from vessels into distant tissues. 5) Formation of dormant micrometastases. 6) Rare colonization of micrometastases into macroscopic tumors limited by the foreign tissue environment. Metastasis suppressor genes and strategies targeting multiple steps simultaneously show promise for preventing cancer spread.

1. DR. MANIN CHAUDHARY
DNB MEDICAL ONCOLOGY 1ST YEAR
23-05-2017
INVASION AND
METASTASIS

2.  The process by which tumor cells from a primary
site invade and migrate to other parts of body is
called metastasis.
 The spread of cells throughout the body results
in physical obstruction, competition with normal
cells for nutrients and oxygen, and invasion and
interference with organ function.

3.  As the bloodstream is the predominant means of
long distance transport, organs in close proximity
“en route” are likely to be main sites of metastasis
for a particular primary tumor.
 “Seed and soil” theory:
Cancer cells = seeds
Optimal environment = soil
 Pre-metastatic niche: as a result of factors
released by the primary tumor, a site of future
metastasis is altered in preparation for the arrival
of tumor cells.

4. The invasion-metastasis cascade
1. Localized invasion
2. Intravasation
3. Transport
4. Extravasation
5. Formation of micrometastasis
6. Colonization

5. The Invasion – Metastasis Cascade

6. 1. Localized invasion
 In order for cells of primary tumor to invade
into their local environment, cells must break
free from the normal molecular constraints
that link adjacent cells to each other (cell
adhesion molecules, E-cadherin, catenin).
 The best characterized alteration involves loss
of E-cadherin by the carcinoma cells
.

7. E-cadherin
 It is an important epithelial cell-to-cell adhesion
molecule, forming adherens junctions between
adjacent epithelial cells .
 Increased expression of E-cadherin is
associated with prevention of invasion and
metastasis, whereas decreased expression is
known to potentiate it.
 The E-cadherin is encoded by the gene CDH1.

9. Matrix metalloproteinases (MMPs)
 Invasion of tumor cells into the surrounding tissue
requires the action of specific proteases that
degrade a path through the ECM and stroma.
 The most important effectors are matrix
metalloproteinases (MMPs).
 In some tumors, invading carcinoma cells make
their own proteases, while in others, bulk of these
proteases are secreted by macrophages, mast
cells and fibroblasts in the tumor stroma.

10. Collaboration of
MT1-MMP and
MMP-2 in
carcinoma

11. The epithelial-mesenchymal
transition (EMT)
 It is a prominent means by which neoplastic
epithelial cells can acquire the ability to
invade, resist apoptosis and disseminate.
 It involves the conversion of a sheet of closely
connected epithelial cells into highly mobile
mesenchymal cells.
 Common in early embryogenesis and in
wound healing, reactivated in cancer cells.

14. Other modes of invasion
 Amoeboid invasion:
• Cancer cells show morphologic plasticity enabling
them to slither though existing interstices in ECM
rather than clearing a path for themselves
 Collective invasion:
• Group of cancer cells advancing in masses into
adjacent tissues
• eg. Squamous cell carcinoma

15. 2. Intravasation
 It is the entry of tumor cell into a blood or
lymphatic vessel.
 It requires several steps:
• Tumor cells must attach to the stromal face of the vessel
• Degrade the basement membrane using MMPs
• Pass between the endothelial cells (transendothelial
migration) into the bloodstream
 Influenced by the structural properties of the blood
vessel : New blood vessels stimulated by tumor;
leaky and tortuous allowing easy access.

16.  The process of intravasation is assisted by
tumor-associated macrophages which guide
tumor cells to the vessels.
 This process involves the CSF-1 receptor on
macrophages and EGF receptor on tumor
cells.
 The tumor cells produce CSF-1 and
macrophages associate with blood vessels to
form EGF leading to chemotaxis-mediated co-
migration.

17. 3. Transport
 Once the cancer cells have intravasated into the
lumen of a blood or lympatic vessel, they may
travel with blood or lymph to other areas of the
body.
 However, cancer cells require anchorage to
solid substrates for survival; without such
attachment, the migrating cells may die of
anoikis.
 The blood represents an actively hostile
environment for metastatizing cancer cells.

18.  Hydrodynamic shear forces in the circulation,
may tear the wandering cancer cells apart.
 The survival of cancer cells in circulation is
greatly enhanced if they can attract a group of
blood platelets, called emboli, to escort them
through the circulation.
 The large size of tumor cells (20-30 µm) relative
to the diameter of capillaries (about 8 µm)
suggests that a large fraction of tumor cells get
trapped in the first capillary beds that they
encounter (first pass organ).

20. 4. Extravasation
 It is the escape of a tumor cell from a blood
vessel or lymphatic vessel, and penetration into
surrounding tissue.
 The steps involved are similar to intravasation,
but in reverse :
• Attachment to endothelial side of blood vessel (E-
selectin)
• Pass through endothelial cells and basement
membrane
• Migrate into surrounding stroma

21. Lodging and extravasation of circulating tumor
cells

22. 5. Formation of micrometastasis
 Once the metastasizing cancer cells arrive within
the tissue parenchyma, they form small clumps or
minute colonies of disseminated cancer cells,
called micrometastasis.
 These micrometastases may lack certain
hallmark capabilities necessary for vigorous
growth, such as ability to activate angiogenesis.
 Moreover, nutrient starvation can induce intense
autophagy that causes cancer cells to shrink and
adopt a state of reversible dormancy.

23.  Such cells can resume active growth and
proliferation when permitted by changes in
tissue microenvironment such as increased
availability of nutrients, or inflammation due to
infection or wound healing.
 Other mechanisms of micrometastatic
dormancy involve antigrowth signals of normal
tissue ECM and tumor-suppressing actions of
immune system.

24. 6. Colonization
 It is the growth of micrometastasis into macroscopic
tumors.
 It is the most difficult step of all, as the foreign tissue
environment do the provide the newly arrived cancer
cells the growth and survival factors, that the primary
tumor provided them.
 Without this physiological support, the metastasizing
cells may die rapidly, or survive for extended periods
as micrometastasis that can only be detected
microscopically, and rarely increase beyond this size.

25.  The probability of an individual cancer cell
successfully completing all the steps of the
invasion-metastasis cascade is very low.
 This low rate of success in forming metastases
is called metastatic insufficiency.
 The earlier steps of this cascade are executed
quite efficiently, while the last step involving
colonization succeeds only rarely, therefore it is
the rate limiting step of the process.

27. Primary tumors and their metastatic
tropisms

28.  Having developed a tissue-specific colonizing
ability, the cells in the metastatic colonies may
proceed to disseminate further, not only to new
sites in the body, but also back to the primary
tumors : self-seeding process.
 The supportive stroma of the primary tumor
provides a hospitable site for reseeding and
colonization by circulating cancer cells.

29. Metastasis suppressor genes
 A new class of genes called metastasis
suppressor genes have been identified.
 They are defined by their ability to inhibit overt
metastasis without affecting the growth of primary
tumor.
 Loss of function of the gene increases the
metastatic propensity of a cancer cell.

30.  NM23 was the first metastasis suppressor gene
to be identified, now 23 such genes have been
identified.
 MKK4 (mitogen activated protein kinase 4) is
another important gene.
 Both promote dormancy of micrometastatic
colonies, and prevent overt metastasis.

31. Strategies for treatment using metastasis
suppressors genes
 Drug development strategies that reactivate
metastasis suppressor genes are being
developed.
 The promoter of NM23 gene is regulated by
glucocorticoid response pathway.
 Medroxy progesterone acetate (MPA), a
progesterone and glucocorticoid agonist was
shown to induce expression of the NM23
promoter.

32. Metalloproteinase inhibitors (MPI)
 Several trials were conducted regarding the
potential development of MPIs as a cancer
treatment drug, but were unsuccessful due to low
efficacy and several side effects.
 No MPIs have received approval for cancer
treatment so far.
 Targeting membrane-bound metalloproteinases by
selective therapeutic antibodies is a more recent
strategy for development of next generation of
metalloproteinase inhibitors.

33. Targeting several steps of metastasis
at once
 Recently, sets of genes or “genes signatures” that
are associated with primary tumor growth and risk of
metastasis have been identified.
 Functions of 4 genes of a lung metastasis gene
signature in human cancer cells were analyzed (the
EFGR ligand epiregulin, COX2, MMP1 and MMP2).
 These 4 genes mediate the processes of tumor
growth, angiogenesis, migration, intravasation and
extravasation.

34.  When all 4 genes were inactivated, tumor
growth and lung metastasis were inhibited.
 A combination of existing drugs was able to
target the protein products of 4 genes and
demonstrated inhibition of growth and
metastasis (Cetuximab: an EGFR antibody;
Celecoxib: a COX inhibitor; and GM6001: A
MMP inhibitor).
 These results hold great potential for the future
and are being developed.

35. THANK YOU