Cell division is essential for healthy growth of an organism and complex genetic mechanisms have evolved to switch cell
division on and off at the proper time for normal development. Cancer happens when cells divide uncontrollably
and produce a growing lump or tumor. Tumors give out chemical signals that prompt the growth
of blood vessels to supply them with oxygen and food. A particularly dangerous aspect of cancer is metastasis. Here, small pieces of the tumor break off and travel
through the bloodstream to invade other parts of the body.