560,000 die of cancer every year in US - 6.6 million worldwide. Cell Growth -In an adult, some cell types can divide but others, muscle and neurons, can't.
Most organs have a reserve of undifferentiated stem cells that can divide in response to injury.
After the damaged area is replaced, cell growth stops. Examples are the small intestine, skin, and blood cells. However, cancer of the small intestine are rare. Growth facotrs turn on cells growth and are tightly regulated. Cell cycle clock is regulated by cyclins and cyclin-dependent kinases .