Part 1 obgyn notes Sri Lanka
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    pathology
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    6.Neoplasia
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    8.INVASION & METASTASIS

    8.INVASION & METASTASIS

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    1. Why this matters

    • Metastasis = spread of malignant tumor from primary site → distant organs
    • Main cause of cancer-related death
    • Requires multiple steps + tumor & stromal cooperation

    A. THE METASTATIC CASCADE – OVERVIEW

    Two major phases

    1. Invasion
      • Tumor breaches ECM + basement membrane at primary site
    2. Vascular dissemination + homing
      • Intravasation → circulation → arrest → extravasation → colonization

    Sequential steps of metastasis

    1. Local invasion
      • Tumor breaks through basement membrane + connective tissue
    2. Intravasation
      • Entry into blood or lymph vessels
      • mediated by proteases + stromal cells
    3. Transport in circulation
      • Tumor emboli protected by platelets and fibrin
    4. Extravasation
      • Exit from circulation → new organ microenvironment
    5. Micrometastasis formation
      • Survival + angiogenic switch
    6. Macrometastasis
      • Progressive growth into clinically detectable secondary tumor

    B. EXTRACELLULAR MATRIX (ECM) BARRIERS

    Barriers tumor must cross

    • Basement membrane at primary tumor
    • Interstitial connective tissue
    • Vascular basement membrane on intravasation
    • Same sequence reversed when colonizing distant organs

    Major ECM components

    • Collagens – mechanical stability
    • Glycoproteins – adhesion molecules (e.g., laminin, fibronectin)
    • Proteoglycans – hydrated gel matrix

    C. FOUR CORE STEPS IN INVASION OF ECM

    Step 1 — LOOSENING CELL–CELL ADHESION

    • Loss of E-cadherin function
    • Mechanisms:
      • E-cadherin gene mutations
      • β-catenin pathway activation
      • Transcription repressors SNAIL & TWIST suppress E-cadherin gene
    • Loss of adhesion enables cells to detach and migrate
    • Prevents normal epithelial anchoring → early trigger of invasion

    Step 2 — LOCAL ECM DEGRADATION

    Who performs degradation?

    • Tumor cells
    • Stromal cells (fibroblasts, inflammatory cells)

    Important proteolytic enzymes:

    • Matrix metalloproteinases (MMPs)
    • Cathepsin D
    • Urokinase plasminogen activator

    MMP-9

    • Cleaves Type IV collagen (major basement membrane component)
    • Releases VEGF, promoting angiogenesis
    • High levels → malignant tumors

    Consequences of degradation

    • Physical path cleared
    • Releases growth factors from ECM stores
    • Produces new substrates favorable for motility

    Step 3 — CHANGES IN ATTACHMENT TO ECM

    Normal epithelial cells:

    • Attach via integrins
    • Loss of ECM contact normally triggers anoikis (apoptosis due to detachment)

    Tumor advantage:

    • Resist anoikis → survive when detached
    • Protease-cleaved ECM fragments generate new binding sites
    • New integrin interactions enhance migration

    Step 4 — LOCOMOTION (CELL MOVEMENT THROUGH ECM)

    Mechanisms:

    • Actin cytoskeleton reorganization
    • Motility proteins + receptors
    • Requires ATP + signaling pathways

    Motility guidance signals:

    • Autocrine motility factors secreted by tumor cells
    • ECM breakdown fragments (e.g., collagen & laminin peptides)
    • Growth factors:
      • IGF-I, IGF-II
      • HGF/SCF from stroma (important at invasive margins)

    D. TUMOR–STROMA INTERACTIONS

    Stroma is active, not passive.

    Stromal contributions to invasion/metastasis:

    • Remodel ECM
    • Secrete proteases and inhibitors
    • Provide growth and motility signals

    Tumor-associated fibroblasts:

    • Alter gene expression
    • Produce:
      • ECM molecules
      • Proteases
      • Protease inhibitors
      • Growth factors

    E. SUMMARY TABLE – ECM INVASION STEPS

    Step
    Main event
    Key mechanisms
    1. Loosening
    Loss of cell adhesion
    ↓E-cadherin (mutation/SNAIL/TWIST)
    2. Degradation
    Break ECM & basement membrane
    MMPs, cathepsin D, urokinase → release VEGF
    3. Attachment change
    Cells interact with new ECM sites
    Tumor resists anoikis
    4. Locomotion
    Move through ECM
    Actin-based crawling guided by growth/ECM signals

    🧠 EXAM REFLEX BLOCK — METASTASIS & ECM INVASION (ZERO-OMISSION)

    Use this as the automatic recall script in MCQs / essays / vivas.

    🔹 Metastasis — Core Definition

    • Metastasis = spread of malignant tumor from primary site → distant organs
    • Main cause of cancer-related death
    • Requires multistep process + tumor–stroma cooperation
    • Benign tumors do not metastasize

    🔹 Metastatic Cascade — Big Picture

    Two phases only (exam favorite):

    1. Local invasion
    2. Vascular dissemination + homing

    🔹 Sequential Steps (Must recall in order)

    1. Local invasion
    2. Intravasation (blood or lymph)
    3. Survival in circulation
    4. Extravasation
    5. Micrometastasis
    6. Macrometastasis
    Order is fixed — rearranged options = trap.

    🔹 ECM Barriers Crossed (Repeated Twice)

    • Basement membrane (primary site)
    • Interstitial connective tissue
    • Vascular basement membrane

      • → Same sequence reversed at distant organ

    🔹 ECM Components — Match Questions

    • Collagen → mechanical strength
    • Glycoproteins (laminin, fibronectin) → adhesion
    • Proteoglycans → hydrated gel matrix

    🧬 FOUR CORE STEPS OF ECM INVASION (HIGH-YIELD)

    STEP 1 — Loosening Cell–Cell Adhesion

    • ↓ E-cadherin = KEY initiating event
    • Mechanisms:
      • E-cadherin gene mutation
      • β-catenin pathway activation
      • SNAIL & TWIST → transcriptional repression
    • Loss of epithelial anchoring → detachment + migration

    Exam trap:

    EMT markers = ↓E-cadherin + ↑motility

    STEP 2 — ECM Degradation

    Who degrades ECM?

    • Tumor cells
    • Stromal cells (fibroblasts, inflammatory cells)

    Key enzymes (memorize list):

    • Matrix metalloproteinases (MMPs)
    • Cathepsin D
    • Urokinase plasminogen activator

    MMP-9 — EXAM FAVORITE

    • Degrades Type IV collagen (basement membrane)
    • Releases VEGF
    • Promotes angiogenesis
    • ↑ in malignant tumors

    Consequences (often asked):

    • Physical invasion path cleared
    • Growth factors released from ECM
    • New ECM fragments → ↑ motility

    STEP 3 — Altered Attachment to ECM

    • Normal epithelial cells → integrin-mediated attachment
    • Detachment → anoikis (apoptosis)

    Tumor advantage:

    • Anoikis resistance
    • Protease-cleaved ECM exposes new binding sites
    • New integrin interactions → ↑ migration

    Exam pearl:

    Survival without ECM attachment = malignant behavior

    STEP 4 — Locomotion

    • Actin cytoskeleton reorganization
    • ATP-dependent
    • Directional migration

    Motility signals:

    • Tumor autocrine motility factors
    • ECM degradation fragments (collagen, laminin peptides)
    • Growth factors:
      • IGF-I, IGF-II
      • HGF / SCF from stroma (invasive margins)

    🧩 Tumor–Stroma Interaction (DO NOT MISS)

    • Stroma = active participant
    • Functions:
      • ECM remodeling
      • Protease production
      • Growth & motility signaling

    Tumor-associated fibroblasts produce:

    • ECM components
    • Proteases + inhibitors
    • Growth factors

    Exam line:

    Tumor progression is bidirectional tumor–stroma crosstalk

    📌 One-Line Ultra-High-Yield Summary

    Metastasis requires sequential loss of adhesion (↓E-cadherin), ECM degradation (MMPs), anoikis resistance, actin-based locomotion, vascular dissemination, and stromal cooperation to form macrometastases.