1. ESCAPE FROM TUMOR IMMUNITY
Insufficient expression of TAA
Insufficient expression of MHC class I
Lack of co-stimulatory signals
Systemic or local immunosuppression
Pro-tumor immune responses
Resistance of tumor cells to immune effector mechanisms
Tumor cells hijack immune checkpoints
Tumor cells fight back (?)

2. Circumventing signals that negatively regulate proliferation (I)
Loss of function of genes that negatively regulate proliferation (mainly tumor suppressors) may lead to cancer
Evasion of contact inhibition
Redirection of TGFβ signaling from proliferation suppression to activation of epithelial to mesenchymal transition (EMT)

4. Circumventing signals that negatively regulate proliferation (II)
Resisting apoptosis by:
-p53 loss of function
-Upregulating expression of anti apoptotic regulators or survival signaling
-Downregulating pro-apoptotic signaling
By inducing inflammation cell necrosis may function to promote tumor progression
Upregulation of autophagy to survive stress and to increase growth and aggressiveness
However
in some cases autophagy may function as an anti cancer mechanism

5. THE TUMOR MICROENVIRONMENT (TME)
Resident cells (e.g. endothelial cells, fibroblasts)
Infiltrating cells (e.g. lymphocytes, macrophages)
ECM (e.g. collagen, fibronectin)
Released molecules (e.g. cytokines, chemokines, antibodies, proteases, angiogenic factors)
Hypoxia
Drugs
These factors may interact with tumor cells & with non-tumor cells in the TME
These interactions regulate gene expression in non-tumor cells and\or cancer cells
Outcome (often): Tumor progression

6. Major hallmarks of tumor-microenvironment interactions (I)
The TME is jointly created by tumor cells, resident and recruited host cells and by secreted products of these cells as well as by non-cellular components of the ECM. Other TME components are degradation products originating in cells residing in the TME
Specific conditions such as hypoxia, low pH or increased interstitial pressure may also exist in the TME
Tumor cells and tumor-derived particles or soluble factors initiate interactions with their immediate microenvironment. These interactions are dynamic and bidirectional and may lead either to further progression, to tumor dormancy or to tumor regression
As a result of such interactions, a dynamic phenotypic reprograming of both interaction partners is likely to occur

7. Major hallmarks of tumor-microenvironment interactions (II)
Tumor-microenvironment interplay with tumor cells often leads to the cooption (hijacking) of physiologic signaling pathways for the survival, propagation and progression of the tumor cells.
The microenvironment of different organs is distinct. The cross-talk between tumor cells infiltrating into a particular organ and the microenvironment of that organ are likely to differ from that occurring in other organs.
Single microenvironmental components may exert pro- or anti-malignancy functions depending on several factors such as tumor stage. The microenvironment of early-stage tumors tends to exert anti-malignancy functions whereas that of late-stage tumors tends to exert pro-malignancy functions.

8. Angiogenesis
Early small tumors use existing vasculature to get nutrients and oxygen and to evacuate waste. As tumors grow, they require more oxygen, nutrients and an efficient system to evacuate waste. This is achieved by vasculature sprouting and neo-vascularization (angiogenesis). An “angiogenic switch” is thus turned on and remains on
The angiogenic switch induces intra-tumoral angiogenesis
Angiogenesis is governed by factors that either induce or oppose this process
The prototype of an angiogenic inducer is vascular endothelial growth factor-A (VEGF-A) and that of an angiogenic inhibitor is thrombospondin-1 (TSP-1) .

9. Angiogenesis regulators in the TME - 1
TABVs= Tumor associated blood vessels

10. Angiogenesis regulators in the TME - 2

11. Angiogenesis regulators in the TME - 3

12. Tumor angiogenesis is regulated by myeloid cells in the TME
-Tumor-derived chemokines recruit immature myeloid cells (MC) to the tumors   These MC may differentiate into TAMs, neutrophils and eosinophils Some MC maintain an immature phenotype in the TME, (monocytic myeloid-derived suppressor cells - M-MDSCs) or granulocytic MDSCs (G-MDSCs) MC promote angiogenesis by producing VEGFA, FGF2 and CXCL EC-derived angiopoietin 2 (ANGPT2) supports angiogenesis in an autocrine manner by binding to the TIE2 receptor

13. Cross-talk between lymphocytes and myeloid cells regulates tumor angiogenesis
Tumor-infiltrating TH2 cells secrete IL-4 and promote the differentiation of TAM to pro-angiogenic M2 TAM TH1 cells and CTL secrete IFNγ stimulating M1 TAM to exert angiostatic functions through CXCL9 and CXCL10. IFNγ also inhibits angiogenesis directly by blocking EC proliferation IgG can stimulate pro-angiogenic macrophage programming via FcγR engagement TAM-derived cytokines IL-10 and TGFβ promote Treg cells that sustain angiogenesis by VEGFA B cells may secrete autoantibodies against pro-angiogenic factors, ANGPT2 and VEGFA, thereby neutralizing their functions and disrupting angiogenesis.

14. Tumors are able to evade VEGF blockage by:
Anti angiogenesis therapy The possibility to target the tumor vasculature was proposed by Folkman already in 1971 Several anti-angiogenesis drugs have been approved by the FDA Antiangiogenic therapy (mainly VEGF blockage) has gained some success but also disappointment.
Tumors are able to evade VEGF blockage by:
-Activation of metabolic or stress responses which enable survival under oxygen and nutrient deprivation -Induction of compensatory pro-angiogenic growth factors such as FGF2 or ANGPT2 -Hijacking the pre-existing vasculature (vascular co-option) -Anti-angiogenic drugs may paradoxically improve blood flow by normalizing the tumor-associated blood vessels

15. Inflammation
Inflammation and immunity are linked through numerous cellular and humoral components as well as through common signaling pathways.
Physiological inflammation participates in the healing process of an injured tissue by:
Recruiting several types of leukocytes to the injured tissue
Angiogenesis
Matrix remodeling
Stimulation of cell growth
An exaggerated and a long-term duration of these processes in tumor-associated inflammation creates a "wound that does not heal“
Cancer and inflammation are linked through 2 mechanisms: Cancer-promoting inflammation chronic inflammation promotes cancer by various mechanisms Cancer-associated inflammation cancer promotes inflammation which, in turn, accelerates cancer progression

16. Inflammation and cancer
Cancer-promoting inflammation Chronic inflammation predisposes patients to cancer and supports carcinogenesis (Rudolf Virchow 1863) Clinical and epidemiological data indicate a significant association between inflammatory bowel diseases and colorectal cancer. The pro-malignant functions of inflammation were strengthened by reports of the beneficial anti-cancer effects of anti-inflammatory drugs Cancer-associated inflammation Signals derived from tumor cells activate immune cells (mainly macrophages) to produce pro-inflammatory Cytokines by: - Recruiting several types of leukocytes to the injured tissue - Angiogenesis - Matrix remodeling - Stimulation of cell growth. In tumor-associated inflammation, an exaggerated and a long-term duration of these processes creates a "wound that does not heal"

18. Disseminatad tumor cells Dormant cells Micrometastasis
The Metastatic Cascade
The microenvironment of the primary tumor
The microenvironment of the specific organ
Cell death
Disseminatad tumor cells Dormant cells Micrometastasis
Growing metastasis
Sharon F. McGee et al (2010), RCSI

19. Genes that enable metastasis formation
In addition to the tumor-initiating events, metastasis requires functionally distinct classes of genes that provide metastasis initiation, progression and virulence functions.
These functions can be acquired through distinct genetic or epigenetic alterations, and might collectively endow circulating cancer cells with the competence to infiltrate, survive in latency and colonize distant organs.

20. Microenvironment evolution – from TME to MME
Figure 4
Microenvironment evolution – from TME to MME
The Cells of the Tumor Microenvironment
(Upper) An assemblage of distinct cell types constitutes most solid tumors. Both the parenchyma and stroma of tumors contain distinct cell types and subtypes that collectively enable tumor growth and progression. Notably, the immune inflammatory cells present in tumors can include both tumor-promoting as well as tumor-killing subclasses.
(Lower) The distinctive microenvironments of tumors. The multiple stromal cell types create a succession of tumor microenvironments that change as tumors invade normal tissue and thereafter seed and colonize distant tissues. The abundance, histologic organization, and phenotypic characteristics of the stromal cell types, as well as of the extracellular matrix (hatched background), evolve during progression, thereby enabling primary, invasive, and then metastatic growth. The surrounding normal cells of the primary and metastatic sites, shown only schematically, likely also affect the character of the various neoplastic microenvironments. (Not shown are the premalignant stages in tumorigenesis, which also have distinctive microenvironments that are created by the abundance and characteristics of the assembled cells.)
Cell  , DOI: ( /j.cell )
Copyright ©

21. Capabilities enabling metastasis
Proliferation
Resisting cell death
Motility & Invasion
Angiogenesis
Metabolism
Inflammation
Escape from immune insults
Main motility & invasion enabling factors: Matrix metalloproteinases (MMPs) & epithelial-mesenchymal transition (EMT)

22. Matrix metalloproteinases (MMPs)
Zinc-dependent endogenous proteases with distinct but partly overlapping substrate specificities and structural similarities
The proteolytic activity of MMPs is regulated by transcription factors, endogenous inhibitors, (TIMPs) and proteases that convert inactive pro-MMPs to enzymatically active MMPs
MMPs are involved in several tumor-supporting cellular processes, including ECM degradation, loss of cell adhesion, angiogenesis, cell proliferation, epithelial-to-mesenchymal transition (EMT) and apoptosis
Thus far MMP inhibitors provided disappointing results in cancer therapy trials

23. MMPs promote both tumor-supporting and tumor-inhibiting functions
From: Matrix metalloproteinases and their clinical relevance in urinary bladder cancer
MMPs exhibit broad substrate specificity, and can promote both tumor-supporting and tumor-inhibiting mechanisms. (1) Breakdown of ECM is a prerequisite of invasive tumor growth, and is necessary for metastasis formation. (2) Proteolytic products of ECM, such as angiostatin, endostatin and neostatin, exhibit potent antiangiogenic properties. However, MMPs can also release proangiogenic factors, such as basic fibroblast growth factor and vascular endothelial growth factor, from their bound, inactive form, thus contributing to tumor angiogenesis. (3) MMPs can activate other MMPs from their pro-enzyme forms by removing their pro-domain. (4) MMPs can process various nonbound proteins. For example, proteolytic degradation of the death ligand FasL helps tumor cells escape from apoptosis, and MMP-mediated inactivation of IGFBPs leads to enhanced IGF activity. (5) MMPs also induce proteolytic shedding of extracellular domains of transmembrane and surface-bound proteins, such as RANKL, E-cadherin, TNF and Fas, enhancing tumor-induced osteolysis and epithelial-to-mesenchymal transition and inhibiting tumor cell apoptosis. Abbreviations: ECM, extracellular matrix; FasL, Fas ligand; IGF, insulin-like growth factor; IGFBP; IGF-binding protein; RANK, receptor activator of nuclear factor κB; RANKL, RANK ligand; TNF, tumor necrosis factor.
MMPs promote both tumor-supporting and tumor-inhibiting functions
(1) ECM degradation is a prerequisite of for metastasis formation
(2) Proteolytic products of ECM, such as angiostatin, endostatin and neostatin, exhibit potent antiangiogenic properties. However: MMPs can also release proangiogenic factors, such as bFGF & VEGF from their inactive form thereby contributing to angiogenesis
(3) MMPs can activate other MMPs from their pro-enzyme forms
(4) MMPs can process various proteins on tumor cells and in the TME. For example, proteolytic degradation of the death ligand FasL helps tumor cells escape from apoptosis
(5) MMPs induce proteolytic shedding of extracellular domains of transmembrane and surface-bound proteins, such as E-cadherin, TNF and Fas, enhancing EMT and inhibiting tumor cell apoptosis.

24. Source of MMPs & tissue inhibitors of metalloproteinases (TIMPs)

25. EMT

26. Epithelial to mesenchymal transition (EMT) & back (MET)

27. Pre-metastatic niche formation
Tumor-derived soluble factors (TSDFs) and extracellular vesicles (EVs) recruit bone-marrow derived cells (BMDCs), myeloid cells, myeloid-derived suppressor cells (MDSCs), Tregs cells, macrophages and neutrophils This platform creates a suitable niche microenvironment for metastatic tumor cell colonization. Hypoxia promotes the formation of the pre-metastatic niche.

28. Characteristics that enable the formation and functions of the pre-metastatic niche

29. The Sentinel Lymph node

30. Is the SLN a marker for metastatic dissemination or a progression-inducing site?

31. Circulating tumor cells

32. CTCs migrate to the premetastatic niche in the distant organ

33. Site-specific metastasis
Tumor cells in one metastatic site differ from tumor cells in other sites or from those in the primary tumor Site specific metastatic signature The metastatic microenvironment of a certain organ differs from the metastatic microenvironment of other organs Microenvironmental signals differ from organ to organ

34. Factors involved in site-specific metastasis

35. The metastatic process

36. CAN METASTASIS BE PREVENTED?
AGAINST:
Too late. Metastases are present already at the time the primary tumor is diagnosed
FOR:
Metastases metastasize.
Prevent metastasis-derived metastasis?

37. Metastasis-derived metastases
Langley & Fidle,r Endocr Rev 2007;28:
Copyright ©2007 The Endocrine Society