BIOLOGY OF INVASION AND METASTASIS: H.A. MWAKYOMA, MD

BIOLOGY OF INVASION AND METASTASIS: For malignant cells to establish a metastasis, a number of steps are required. 1.Invasion of the basement membrane underlying the tumour. 2.Movement through the extracellular matrix 3.Penetration of the vascular or lymphatic channels 4.Survival and arrest within the circulatory blood and lymph. 5.Exit from the circulation (Extravasation) into a new tissue site

How do cells move through tissues? Acquire invasive ability Ability to degrade extracellular matrix (ECM) Acquire motile ability Lose cell-cell junctions (EMT-like switch) Acquire motile capability Directed migration to hospitable sites Chemotaxis Communication between tumor and host cells

The three steps of invasion 2 1. Matrix degradation Matrix attachment 3 Locomotion Tumor invasion and metastasis-role of the extracellular matrix.

Components of invasion Matrix degrading enzymes Cell adhesion Cell motility

Extracellular matrix [ECM] A meshwork of proteins secreted by cells structural support reservoir for signaling factors source of information for cells. A. Basement membrane specialized ECM found at the basal surfaces of epithelia, endothelia and muscle cells thin sheet (40-120nm) of dense, organized ECM matrix protein B. ECM of connective tissue surrounds fibroblastic/stromal cells

1.Invasion of the basement membrane underlying the tumour Penetration of the basement membrane of the host tissue and the invasion of the surrounding extracellular environment is believed to involve 3 steps. Binding of the extracellular matrix: The initial binding tumour cells involve such tissue matrix components such as; Fibronectin Laminin and Proteoglycans NB: Particular attention has been paid to the interaction of Laminin receptors on the surface of cancer cells with the basement membrane

(i)Binding of the extracellular matrix: Other molecules implicated in the binding of tumour cells to matrix components are a family of cell surface glycoproteins termed Integrins

(ii) Degradation of extracellular matrix: After binding of matrix components, the invading tumour cells SECRETE ENZYMES that degrade matrix components such as Collagen type IV Fibronectin Proteoglycans

Degradation of extracellular matrix: The major types of protease are serine protease Collagenase (Metalloprotease) Cysteine protease All the are produced by cancer cells.

(ii) Degradation of extracellular matrix: Tumour cells also secrete type IV collagenase and Stromelysin (Another Metalloprotease) Malignant cells can stimulate the secretion of Type I collagenase by fibroblasts. Cathepsin B – a lysosomal cystein protease has broad spectrum activity against many proteins including; Laminin, Fibronectin and Type IV collagen. NB: The activity of this enzyme in human tumours has been correlated with their metastatic potential.

(iii) Movement through interstitial tissues: Many of the steps in the metastatic cascade require locomotion by malignant cells The Autocrine Motility Factor (AMF) induces the protrusion of pseudopodia which are enriched in receptors for laminin and fibronectin. Thus, AMF appears to stimulate the cell locomotion, promote an interaction with matrix proteins and dissolution of the matrix.

METASTASIS Following the invasion of the surrounding tissue, malignant cells may spread to distant sites by a process that includes a number of steps (Metastatic cascade):

What is cancer metastasis? Metastasis – Greek for “beyond place” Cancer defines as a population of cells that have lost their normal controls of growth and differentiation and are proliferating without check. Metastasis is the process by which a tumor cell leaves the primary tumor, travels to a distant site via the circulatory system, and establishes a secondary tumor.

5 major steps in metastasis Invasion and infiltration of surrounding normal host tissue with penetration of small lymphatic or vascular channels; Release of neoplastic cells, either or single cells or small clumps, into the circulation; Survival in the circulation; Arrest in the capillary beds of distant organs; Penetration of the lymphatic or blood vessel walls followed by growth of the disseminated tumor cells

1. INVASION OF THE CIRCULATION: (a) After invading the interstitial tissue, malignant cells penetrate vascular or lymphatic channels. The majority of tumour cells do not survive their journey in the blood stream and less than 0.1% remain to establish a new colony. The presence of malignant cells in blood or lymph does not mean that metastases will inevitably develop.An overwhelming majority of tumour cells released in the blood die very quickly.

1. INVASION OF THE CIRCULATION (b) Formation of clumps: while in the bloodstream, the malignant cells may; adhere to the tumour cells to for clumps Adhere to platelets or lymphocytes Enter capillary bed in which they may impact. Adhere to capillary endothelium Formation of secondary deposit may occur

1. INVASION OF THE CIRCULATION (c) Fibrin formation: After impaction in small blood vessels (capillaries), some tumour cells stimulate the production of fibrin- which tends to protect (Evasion) the clump of malignant cells and enable them to proliferate.

2.ESCAPE FROM THE CIRCULATION: ( Migration from the vascular compartment) Circulating tumour cells may be arrested mechanically in capillaries and venules (Impaction) where they attach (Attachment) to the endothelial cells. The adherence causes Retraction of the endothelium, thereby posing the underlying basement membrane, to which the tumour cells now bind and create a free space through which tumour cells escape.

2.ESCAPE FROM THE CIRCULATION: Clumps of tumour cells may also be arrested in arterioles where they grow within the vascular lumen. In both situations, the tumour cells eventually extravasate (Extravasation) by a mechanism similar to those responsible for local invasion.

ESTABLISHMENT OF NEW LOCAL GROWTH ( Survival at the new site) Within the extracellular tissues, a new and suitable microenvironment must be established if the colony of the tumour cells is to grow and flourish. In a hospitable site, the extravasated cells grow in response to autocrine and possibly local growth factors produced by the host tissue.

ESTABLISHMENT OF NEW LOCAL GROWTH ( Survival at the new site) If the colony is to grow to a significant size, a new blood supply must be available both for nutrition of the tumour cells and for carrying away cellular waste products. The new blood vessels are derived from host’s vasculature Ingrowth of blood vessels is stimulated by the secretion of large molecules (Polypeptides) from tumour cells termed as Tumour Angiogenesis factors which may include;

ESTABLISHMENT OF NEW LOCAL GROWTH ( Survival at the new site) Platelet- derived growth factor (PDGF) Fibroblast growth factor (FGF) Transforming growth factor β (TGF-β) – this stimulates the growth of new blood vessels in the host tissue a process termed as ANGIOGENESIS. Establishment of metastatic colony must escape detection and destruction by the host immune defenses (EVASION). The metastatic colony may not enlarge (Tumour dormancy)

ROUTES OF METASTASIS: Cancers may spread to distant sites by the following pathway. Lymphatic spread Haematogenous spread Other routes (i) Transcoelomic spread (ii) Spread along epithelium-lined surfaces (iii) Spread via cerebrospinal fluid (iv) Implantation

ROUTES OF METASTASIS: 1. Lymphatic spread: In general carcinomas metastasise by lymphatic route while sarcomas favour haematogenous route. However, sarcomas may also spread by lymphatic spread.

ROUTES OF METASTASIS: 2. Haematogenous spread: Metastasis through blood vessels is the common route for sarcomas but certain carcinomas also frequently metastasise by this mode. The common sites for blood-borne metastasis are the liver, lungs, kidneys, brain and bones; all of which provide “good soil” for growth of “good seeds” (Seed-soil theory) than are the unfavourable sites like the spleen and muscles

ROUTES OF METASTASIS: 3. Other routes of metastasis: (i) Transcelomic spread:- Certain cancers invade through the serosal wall of the coelomic cavity so that tumour cells break from the cluster and spread by coelomic fluid and are implanted elsewhere in the body cavity. Peritoneal cavity is involved most often, but occasionally pleural and pericardial cavities are also affected. Transcoelomic spread in peritoneum by carcinoma of the stomach and ovary are important example (Krukerberg tumour). Pleura and pericardium are often involved by carcinoma of the bronchus and breast

3. Other routes of metastasis: (ii) Spread along epithelium-lined surfaces:- Malignant tumours may spread through the fallopian tube from the endometrium to the ovaries or vice versa; through the bronchus into alveoli; and through the ureters from the kidneys into lower urinary tract.

3. Other routes of metastasis: (iii) Spread via cerebrospinal fluid:- Malignant tumours of the ependyma and leptomeninges may spread by release of tumour fragments and tumour cells into the CSF and produce metastases at the sites in the CNS (iv) Implantation:- Rarely a tumour may spread by implantation by surgeon’s scapel, needles, sutures or my be implanted by contact.

THE PATTERN OF METASTASIS: Why do metastases establish where they do? Mechanical/Anatomical hypothesis - Ewing First capillary bed reached: cells trapped in small vessels “Seed and soil” hypothesis - Paget Importance of microenvironment to tumor growth “When a plant goes to seed, its seeds are carried in all directions; but they can grow only if they fall on congenial soil (Homing mechanism),

THE PATTERN OF METASTASIS: Reason for organ selectivity Mechanistic theory: determined by the pattern of blood flow. “Seed and soil” theory: the provision of a fertile environment in which compatible tumor cells could grow

Molecular mechanisms of organ site preference Endothelial cell surface receptors Organ-specific chemoattractants Organ-specific growth factors Different tumour cells would thrive in certain “Biological soils” but not others. This may be due to:- Appropriate growth factors or extracellular matrix environment Compatible adhesion sites on the endothelial lumenal surface Selective chemotaxis at which the organ producing some soluble attraction factors to the tumor cells

Molecular mechanisms of organ site preference

THE PATTERN OF METASTASIS Some common patterns of metastasis in human tumours include; 1. THE LIVER This is the site in which blood-borne metastases occurs most frequently. E.g. Pancreatic, GIT tumours- due to venous drainage via Portal system 2. LUNGS Tumours which favour to spread to this site include; carcinoma of the breast, carcinoma of the stomach and sarcomas.

THE PATTERN OF METASTASIS 3. THE SKELETON After the liver and lungs, the skeleton is the most frequent site for metastasis deposits to occur. Common sites of origin of the tumours are Lungs, breast, prostate, kidney and thyroid. Bony metastases may either elicit the production of new bone (Osteoblastic) or destroy bone (Osteolytic)

Bony metastases----- Osteoblastic tumours – the secondary deposits are very hard. Examples: carcinoma of the prostate. Osteolytic tumours – secondary deposits cause bone destruction. Examples are Multiple myloma.

THE PATTERN OF METASTASIS 4. BRAIN Secondary deposits occur quite frequently in brain The lung is one of the most common primary site

THE PATTERN OF METASTASIS THE ADRENAL GLAND Of all endocrine organs, the adrenal is the most frequently involved by metastatic tumours. The medulla is the most favoured site of metastases. Common primary site for adrenal secondaries include the lungs and breast.

Organ site preference for metastasis (Summary) Lung and liver: common sites of metastasis Colon adenocarinoma Liver Breast adenocarcinoma Bone, brain, adrenal Prostate adenocarcinoma Bone Lung: SCLC Bone, brain, liver Melanoma - cutaneous Brain, liver, colon Thyroid adenocarcinoma Bone Kidney clear cell carcinoma Bone, liver, thyroid Testis carcinoma Liver Bladder carcinoma Brain Neuroblastoma Liver, adrenal