Metastasis involves the spread of tumor cells from a primary site to distant sites with continued relentless growth. Metastasis is responsible for about 90 percent of cancer deaths and is the most fearsome aspect of cancer. The epithelial mesenchymal transition is currently the dominant explanation for the origin of cancer metastasis and is based on the somatic mutation theory of cancer. However, emerging evidence indicates that metastatic cancer cells arise following the fusion of cancer stem cells with macrophages.
Read MoreIs Cancer a Genetic or Metabolic Disease? Part 4Third-class levers are plentiful in human anatomy, with the elbow and biceps brachii combining to provide the most commonly used example.
Just as there are many remote causes of plague—heat, insects, rats—but only one common cause, the plague bacillus, there are a great many remote causes of cancer—tar, rays, arsenic, pressure, urethane—but there is only one common cause into which all other causes of cancer merge: the irreversible injuring of respiration.
A third-class lever is another simple machine comprising a beam placed upon a fulcrum. In the third-class lever, the fulcrum is placed at one end of the beam, a load is placed at the other end, and the effort is applied between them in a direction counter to the force of the load.
Read MoreAnatomy of Levers, Part 4: Third-Class Levers