How cancer spreads

19^th January 2018

Cancer cells differ from normal cells in several ways, one of which is that cancer cells are able to detach from nearby cells in order to invade and spread to other tissues. Normal cells make adhesion molecules which act like glue, holding similar cells together. Cancer cells lack these adhesion molecules allowing them to break loose and travel. Another difference is that normal cells communicate with other nearby cells—in essence, being reminded of their boundaries. Cancer cells have devised ways to ignore these communication signals. Once a cancer cell is “loose” and mobile, it is able to travel. There are several different ways in which cancer cells spread:

• Locally (regionally): When benign tumors grow they do so as a solid mass, as if there is a clear boundary containing them.  In contrast, cancer cells invade neighbouring tissues in an invasive manner which can appear like tentacles.  It is, in fact, the claw-like extension of cancer into other tissues from which the name originates; cancer being derived from the Greek word for claw.
  
  
• Through the bloodstream: Cancer cells can enter the bloodstream and travel to other regions of the body.
  
  
• Through the lymphatic system: The lymphatic system is another network through which cancer cells can travel.

• Through the airways (lung cancer): In addition to the methods of metastasis above, recent studies suggest that lung cancer, likely spreads through the airway of the lungs (aerogenous metastasis) as well, and this may be even more important than bloodstream metastasis for people with lung adenocarcinoma.

Cancer cells work in many more ways to fool or coerce the body into actions that will destroy the host. More of this later.