In-depth Notes on Tumor Progression and Metastasis

Tumor Progression and Metastasis

  • Carcinogenesis

  • Defined as the process by which normal cells transform into cancerous cells, leading to loss of crucial regulatory elements.

  • As tumor cells grow and divide, they accumulate additional mutations.

  • These mutations facilitate tumor progression and may eventually result in invasion and metastasis.

  • Hallmark of Cancer

  • Malignant tumors invade locally and spread to distant sites (known as metastasis).

Characteristic Changes for Tumor Spread
  1. Down Regulation of E-cadherin
  • E-cadherin is a molecule that helps cells adhere to one another.
  • Importance: Tumor cells must dissociate from neighboring cells to spread.
  • Down-regulating E-cadherin allows tumor cells to lose adhesion and begin their spread.
  1. Attachment to Laminin
  • After losing connection with neighboring cells, tumor cells attach to laminin present in the basement membrane.
  • Basement membrane is primarily composed of collagen IV and laminin.
  1. Destruction of Basement Membrane
  • Tumor cells can secrete collagenase (especially type IV) that degrades collagen IV in the basement membrane.
  • This process is crucial for allowing tumor cells to invade further.
  1. Attachment to Fibronectin
  • Once the basement membrane is breached, tumor cells attach to fibronectin in the extracellular matrix (ECM).
  • Enables further local spread of tumor cells.
  1. Entering Vascular or Lymphatic Systems
  • Tumor cells gain access to blood vessels or lymphatics which allows for distant spread.
  • Types of Spread:
    • Lymphatic spread (common in carcinomas).
    • Hematogenous spread (characteristic of sarcomas).
Spread Patterns of Tumors

  • Carcinomas

  • Typically spread via lymphatics to regional lymph nodes.

  • Example: Breast cancer often spreads to the axillary lymph nodes.

  • Sarcomas

  • Usually spread through hematogenous routes to distant sites.

  • Examples include osteosarcoma (bone), chondrosarcoma (cartilage), and liposarcoma (adipose tissue).

Exceptions in Tumor Spread

  • Certain Carcinomas that Spread Hematogenously

  • Renal Cell Carcinoma: Invades renal veins, leading to distant metastases.

  • Hepatocellular Carcinoma: Invades hepatic veins, spreading through blood.

  • Follicular Carcinoma of the Thyroid: Spreads through blood vessels.

  • Choriocarcinoma: Malignancy originating from trophoblasts, which naturally invade blood vessels.

  • Seeding of Body Cavities

  • Ovarian Carcinoma is known for seeding body cavities; often involves the omentum.

  • Classic presentation referred to as "omentum caking," where cancerous spread leads to thickened omental tissue resembling cake.