cancer metastasis

Cancer Metastasis and Cell Migration/Invasion

Cancer metastasis is the multi-step process by which cancer spreads from its primary site to distant organs. It is essentially normal cell migration and tissue invasion hijacked by mutated cells.

The metastatic cascade involves several key stages driven by migration and invasion:

• Loss of Adhesion and Local Invasion: In a healthy epithelial tissue, cells stick together tightly via adhesion molecules (like E-cadherin). Cancer cells often acquire mutations that downregulate these adhesion molecules. By losing their grip on neighbors, they can break through the basement membrane and invade neighboring tissues using enzymes called matrix metalloproteinases (MMPs) to chew through the extracellular matrix.

  ​They actively lose cell-cell adhesion: Cancer cells aren't just passively "weak." They actively shut down the production of adhesion molecules (like E-cadherin) that normally act like velcro keeping cells tightly locked to their neighbors. By turning these off, they intentionally let go of each other so they can break free.

  The enzymes chew the surroundings, not the cells: The enzymes (like matrix metalloproteinases or MMPs) don't usually chew the neighboring cells themselves. Instead, they chew through the extracellular matrix and the basement membrane—the tough, mesh-like structural "walls" and scaffolding that trap tissues in their proper place.

• Intravasation: Driven by directional chemical signals (chemotaxis), the migrating cancer cells squeeze through the walls of local blood or lymphatic vessels to enter the circulation.

• Circulation and Extravasation: The cells travel through the bloodstream. Once they reach a distant organ, they migrate back out of the blood vessels (extravasation) into the surrounding tissue parenchyma.

• Colonization (Secondary Tumors): The migrated cancer cells adapt to the new microenvironment, proliferate, and establish secondary tumor colonies.

Key Difference: While normal cell migration is tightly regulated by checkpoints, stop signals, and precise chemical cues, cancer invasion and metastasis represent unregulated, destructive migration that ignores normal tissue boundaries.