Metastasis

Slide 1 · Metastasis

Biologic foundations and clinicopathologic interpretation

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Define metastasis and distinguish it from contiguous local invasion.

Explain variation in metastatic behavior among malignant tumors.

Relate dissemination routes to anatomy, tumor biology, and examination of regional nodes.

Follow the principal steps from matrix invasion to colonization.

Slide 3 · A precise definition

Spread of a primary tumor to physically discontinuous sites

This finding unequivocally establishes malignant behavior.

Slide 4 · Discontinuous spread: The essential feature

Primary tumor

Transport or dissemination

Separate tumor deposit

The secondary focus is not simply direct extension of the primary mass.

Physical separation is the defining spatial distinction.

Slide 5 · Primary tumor and metastatic deposit

Primary tumor

Original neoplasm at the site of origin.

Metastatic deposit

Tumor at a physically separate site derived from the primary.

A metastatic focus is malignant even when its morphology is well differentiated.

Slide 6 · Metastasis is a decisive marker of malignancy

Benign neoplasms lack the capacity to establish true metastases.

The finding is stronger evidence of malignancy than growth rate or apparent circumscription.

An absence of detectable metastases does not establish benignity.

Slide 7 · Invasion and metastasis are distinct properties

Local invasion

Tumor infiltrates contiguous surrounding tissues.

Metastasis

Tumor establishes a separate focus at a distant or noncontiguous site.

A tumor may invade early yet metastasize only rarely.

Slide 8 · How invasion creates access to dissemination

Invade adjacent tissue

Enter lymphatics, blood vessels, or cavities

Reach a separate site

Invasion creates opportunities for spread; It does not guarantee successful colonization.

Slide 9 · Benign masses usually remain localized

Benign pattern

Expansile, often circumscribed growth; No distant spread.

Malignant pattern

Infiltration across tissue planes; Possible distant deposits.

A capsule or smooth border alone is not a universal discriminator.

Slide 10 · Why local invasion matters even without spread

Destruction of adjacent structures can cause morbidity without metastasis.

Infiltrative margins make complete excision more difficult.

Local behavior and metastatic potential require separate assessment.

Slide 11 · Malignant tumors differ in metastatic frequency

Malignant tumors have metastatic potential, but expression of that potential varies widely.

Many carcinomas spread readily; Selected invasive cancers seldom disseminate.

A universal rate or timetable cannot be assigned to “malignancy.”

Slide 12 · Gliomas illustrate an important exception

Glial malignancies within the central nervous system can be highly locally invasive.

Despite invasion, extracranial metastases are uncommon.

Clinical severity can reflect local destruction rather than systemic deposits.

Slide 13 · Basal cell carcinoma illustrates another exception

Basal cell carcinoma is malignant and can invade adjacent tissue.

Distant metastasis is very rare.

Its malignant classification does not depend on frequent systemic spread.

Slide 14 · Why those exceptions matter

Incorrect inference

“Rarely metastasizes” means the lesion must be benign.

Correct inference

Invasiveness and metastatic dissemination are biologically separable.

Do not use a single behavior in isolation to classify a tumor.

Slide 15 · Hematologic malignancies are a special case

Leukemias and lymphomas derive from cells capable of physiologic circulation.

They often involve multiple anatomic sites at presentation.

Their malignant status does not require the solid-tumor pattern of metastasis.

Slide 16 · Solid tumors versus blood cancers

Solid tumors

Arise from cells not normally circulating freely; Spread is acquired.

Leukemia / lymphoma

Arise from lineages naturally trafficking through blood or lymphoid tissues.

“Disseminated” is not interpreted identically across these tumor classes.

Slide 17 · Metastatic disease at presentation

≈ 30%

Approximately 30% of solid tumors present with metastatic disease.

Robbins estimate; Excludes skin cancers other than melanoma.

Slide 18 · Interpreting the textbook estimate

The figure describes metastatic disease already present at diagnosis.

It is not the lifetime probability that every solid tumor will metastasize.

The stated exclusion prevents direct application to all cancers combined.

Slide 19 · Features broadly correlated with metastasis

Increased likelihood of metastasis

Poor differentiation

Aggressive local invasion

Rapid growth

Large tumor size

Slide 20 · Poor differentiation: An association

Loss of differentiation commonly accompanies more aggressive tumor biology.

Undifferentiated appearance is a correlate—not proof—of metastatic spread.

Morphology must be interpreted alongside actual stage and observed behavior.

Slide 21 · Aggressive local invasion: An association

Extensive infiltration signals ability to overcome tissue barriers.

Tumors breaching boundaries may gain access to vascular and lymphatic channels.

Invasion provides opportunity; Distant colonization is a further hurdle.

Slide 22 · Rapid growth: An association

Rapidly enlarging malignant tumors more often exhibit aggressive behavior.

Kinetic appearance alone cannot predict whether metastases are present.

Some slow-growing tumors nevertheless develop widespread deposits.

Slide 23 · Large size: An association, not a rule

Increasing primary tumor size often correlates with metastatic likelihood.

Size does not fully capture the tumor’s metastatic competence.

A small neoplasm can already have metastasized.

Slide 24 · Small tumors can spread widely

Primary lesion

Small; Sometimes well differentiated and slow growing.

Clinical observation

May nevertheless show extensive metastatic deposits.

Do not equate a reassuring primary appearance with absence of metastasis.

Slide 25 · Large tumors may remain localized

Primary lesion

Large and rapidly growing.

Clinical observation

May remain confined to the primary site.

Metastatic competence cannot be inferred from size alone.

Slide 26 · No simple metastatic prediction score

Metastatic outcome

Primary morphology

Growth and invasion

Tumor–host interactions

Slide 27 · Tumor and host both influence spread

Metastatic outcome

Cancer-cell properties

Tissue barriers

Circulatory survival

Target-organ microenvironment

Slide 28 · Why metastasis changes prognosis

Separate deposits indicate disease outside the primary tumor bed.

Complete local excision alone may not eliminate disseminated disease.

Metastatic spread strongly reduces the possibility of cure.

Slide 29 · Metastasis may precede first diagnosis

A clinically apparent primary lesion may already have seeded distant sites.

Interventions that only prevent later cell escape may be too late in some patients.

Early detection and systemic disease assessment therefore remain important.

Slide 30 · Three principal routes of dissemination

Cancer dissemination

Body cavity / surface seeding

Lymphatic dissemination

Hematogenous dissemination

Slide 31 · Seeding onto open body surfaces

Tumor reaches open cavity

Detached malignant cells

Surface implantation

The peritoneal cavity is commonly involved.

Pleura, pericardium, meninges, and joints can also be affected.

Slide 32 · Ovarian carcinoma: Peritoneal seeding

Ovarian carcinomas characteristically disseminate across peritoneal surfaces.

Serosal and omental deposits may produce extensive surface coating.

This is transcoelomic spread rather than a contiguous mass alone.

Slide 33 · Pseudomyxoma peritonei: An example

Certain mucin-producing appendiceal or ovarian carcinomas disseminate within the peritoneal cavity.

A gelatinous neoplastic mass can accumulate in the peritoneal space.

Pseudomyxoma peritonei to illustrate surface seeding.

Slide 34 · Lymphatic spread of carcinomas

Invasive carcinoma

Peripheral lymphatic vessels

Regional draining lymph nodes

Most common initial dissemination pathway for carcinomas.

Sarcomas can also use lymphatic dissemination.

Slide 35 · Lymphatics at invasive tumor margins

Functional lymphatics at the invasive perimeter enable tumor-cell entry.

Those marginal channels from functional vessels within the tumor.

Routes reflect local anatomy and regional drainage.

Slide 36 · Breast carcinoma: A drainage example

Primary breast carcinoma

Axillary nodes

Infraclavicular / supraclavicular nodes

The described sequence is typical, not inevitable.

Node evaluation has prognostic and therapeutic relevance.

Slide 37 · Lung carcinoma: A drainage example

Primary bronchial carcinoma

Perihilar / tracheobronchial nodes

Mediastinal nodes

The anatomical location of the primary shapes expected nodal stations.

Slide 38 · Skip metastasis

Expected pattern

Sequential spread through an adjacent regional node basin.

Skip pattern

A more distant node is involved while an expected station is not identified as involved.

Variable drainage and possibly missed microscopic disease.

Slide 39 · What is a sentinel lymph node?

The first node in a regional basin receiving lymphatic drainage from a primary tumor

Its evaluation samples an early nodal route of dissemination.

Slide 40 · Sentinel-node mapping: Rationale

Map primary drainage

Identify first draining node

Microscopic node assessment

Radiolabeled tracers or dyes can map drainage.

Sampling can reduce the need for extensive regional dissection in selected settings.

Slide 41 · An enlarged regional node is not always metastatic

Metastatic involvement

Malignant tumor cells are found within nodal tissue.

Reactive hyperplasia

Immune stimulation enlarges the node without metastatic tumor.

Microscopic examination resolves the distinction.

Slide 42 · Hematogenous dissemination

A typical route for sarcomas; Also occurs in carcinomas.

Histologic vascular invasion is an ominous feature.

Tumor cells commonly penetrate small veins; Arterial walls are more resistant.

Slide 43 · Why venous invasion is prominent

Tumor enters small vein

Tumor embolizes with blood flow

Cells arrest in a downstream capillary bed

The first capillary filter often influences organ distribution.

Slide 44 · Portal venous drainage predicts liver deposits

Gastrointestinal primary

Portal venous circulation

Liver capillary bed

Colon cancer has a strong anatomical pathway for hepatic metastasis.

Slide 45 · Systemic venous drainage predicts lung deposits

Systemic venous tumor embolus

Right heart

Pulmonary capillary bed

Lung is a common site of blood-borne deposits.

Slide 46 · A vertebral route of dissemination

Tumor near vertebral column

Paravertebral venous plexus

Vertebral metastasis

Thyroid and prostate carcinomas as examples.

Slide 47 · Vascular drainage does not explain everything

Metastatic organ patterns can be characteristic of individual cancer types.

Some preferred sites are not predicted by first-pass vascular filtration.

Tumor–endothelial and tumor–tissue interactions also matter.

Slide 48 · Venous extension is not identical to widespread metastasis

Renal cell carcinoma

May grow along renal vein into inferior vena cava.

Hepatocellular carcinoma

May extend into portal or hepatic venous channels.

Extensive intravascular growth may occur without proportionate distant deposits.

Slide 49 · The metastatic cascade

Local invasion

Intravasation / survival

Extravasation

Distant growth

A successful metastatic deposit requires completion of multiple distinct steps.

Each step can restrict overall success.

Slide 50 · Matrix barriers are encountered twice

At the primary site

Cancer traverses epithelial and vascular basement membranes to intravasate.

At the secondary site

Cancer crosses vessel-associated barriers to invade new tissue.

Interstitial extracellular matrix lies between these boundaries.

Slide 51 · Four steps in local extracellular-matrix invasion

1. Reduced cell–cell adhesion

2. Proteolytic remodeling of ECM

3. Attachment to altered ECM

4. Cell migration through matrix

Slide 52 · E-cadherin and epithelial cohesion

E-cadherin mediates homotypic adhesion between epithelial cells.

Reduced adhesion can permit detachment of neoplastic cells.

In selected cancers, mutation or altered expression disrupts E-cadherin function.

Slide 53 · Epithelial–mesenchymal transition: Proposed role

Epithelial program

E-cadherin-mediated cohesion and epithelial differentiation markers.

Mesenchymal-like program

SNAIL / TWIST-associated changes; Vimentin and motility-associated features.

EMT as an implicated mechanism, not a universal prerequisite.

Slide 54 · Proteases remodel tissue barriers

Tumor / stromal proteases

Collagen and matrix degradation

Invasive passage

MMPs, cathepsins, and urokinase plasminogen activator are implicated.

Proteolysis can also liberate matrix-sequestered growth signals.

Slide 55 · Matrix remodeling can amplify invasion

MMP2 and MMP9 cleavage of laminin and type IV collagen exposes new binding sites.

MMP9 can release extracellular-matrix-bound VEGF.

The degraded matrix is not simply a passive gap; It can generate bioactive signals.

Slide 56 · Integrins, attachment, and anoikis

Integrins connect cells to extracellular matrix and transmit survival cues.

Loss of anchorage normally can initiate anoikis, a form of apoptosis.

Tumor cells that resist anoikis can survive detachment and altered matrix attachment.

Slide 57 · Locomotion is an active process

Leading-edge attachment

Actin cytoskeletal contraction

Trailing-edge detachment

Migration depends on coordinated adhesion, cytoskeletal change, and signaling.

Tumor-derived and stromal motility signals may guide movement.

Slide 58 · Microenvironmental partners in invasion

Invading cancer cells

Cancer-associated fibroblasts

Inflammatory cells

Endothelial cells

Extracellular matrix

Slide 59 · Intravasation: Entering vascular space

Tissue invasion

Vascular basement-membrane breach

Entry into vessel lumen

The invasion programme provides physical access to hematogenous spread.

Slide 60 · Survival in blood is a bottleneck

Circulating tumor cell

Shear stress

Anoikis

Innate immune attack

Adaptive immune attack

Slide 61 · Clusters may support circulating tumor cells

Evidence favoring multicellular aggregates in metastatic establishment.

Interactions with platelets may help stabilize and protect tumor emboli.

Circulating cells are commoner than successful metastatic colonies.

Slide 62 · Three determinants of distant deposits

Sites of metastasis

Primary-site drainage

Organ-specific tropism

Escape from dormancy

Slide 63 · Organ tropism beyond anatomic flow

Some tumors preferentially metastasize to selected organs.

Adhesion molecules and chemokine receptors can contribute to selective homing.

The new organ’s microenvironment must also support cancer-cell survival.

Slide 64 · The seed-and-soil concept

Seed

Circulating cancer cells with properties enabling survival and growth.

Soil

A receptive target-organ stroma and extracellular environment.

Highly vascular tissues are not uniformly permissive to metastasis.

Slide 65 · Extravasation at the secondary organ

Vascular arrest

Transendothelial migration

Basement-membrane passage

Tissue implantation

Adhesion molecules, proteases, and chemokines can contribute.

Mechanisms differ by target-organ endothelium.

Slide 66 · Tumor dormancy: Surviving without expansion

Microscopic survival

Tumor cells remain at a distant site without a growing clinical lesion.

Overt metastasis

Colonization progresses to a clinically significant tumor deposit.

Dormancy is described in melanoma, breast carcinoma, and prostate carcinoma.

Slide 67 · Metastatic colonization depends on host stroma

Cancer-derived signals can alter resident stromal cells at a secondary site.

The modified stroma can supply matrix and growth factors supporting expansion.

Survival after extravasation is not equivalent to successful outgrowth.

Slide 68 · Bone metastasis: A reciprocal growth circuit

Tumor-derived PTHRP

Osteoblast RANKL

Osteoclast activation

Matrix growth-factor release

Released IGF and TGF-β can further support tumor growth.

Slide 69 · Clinical application: An invasive basal cell carcinoma

A skin lesion shows infiltrative malignant basaloid growth. There is no evidence of distant disease.

Does the absence of metastasis invalidate its classification as malignant?

No. Basal cell carcinoma can invade locally yet metastasize very rarely.

Slide 70 · Clinical application: A small distant-spreading tumor

A relatively small, well-differentiated primary malignancy is associated with lesions in separate organs.

Does small size or good differentiation exclude metastasis?

No. Robbins explicitly describes small, well-differentiated tumors that metastasize widely.

Slide 71 · Clinical application: An enlarged draining node

A carcinoma drains to a palpable enlarged regional lymph node.

Can enlargement alone establish nodal metastasis?

No. Reactive hyperplasia is another explanation; Microscopic assessment is needed.

Slide 72 · Five distinctions to retain

Term

Working interpretation

Metastasis

Physically discontinuous neoplastic deposit

Local invasion

Contiguous infiltration at primary site

Lymphatic spread

Transport through regional lymphatic drainage

Hematogenous spread

Transport through blood with vascular arrest

Colonization

Successful growth at a secondary site

Slide 73 · Selected source reading

Robbins, Cotran & Kumar: Pathologic Basis of Disease. 11th ed. Chapter 7, “Neoplasia.”

Core teaching unit: “Metastasis,” p. 242.

Contextual sections: “Pathways of Spread,” pp. 243–244; “Invasion of Extracellular Matrix,” pp. 274–275; “Vascular Dissemination, Homing, and Colonization,” pp. 275–276.