In this section you will learn:
Cancer is not one disease; it is a collection of many diseases characterized by the uncontrolled growth of cells.
Changes in the genetic material in a normal cell underpin cancer initiation and development in most cases.
A cancer cell’s surroundings influence the development and progression of disease.
The most advanced stage of cancer, metastatic disease, accounts for more than 90 percent of cancer deaths.
The more we know about the biology of cancer, the more precisely we can prevent, detect, diagnose, and treat it.
Cancer is not one disease; it is a collection of many diseases that arise when the processes that control the multiplication and life span of normal cells go awry.
As humans develop, we grow, through extensive cell multiplication, from a single cell to an estimated 37.2 trillion cells in an adult body (20). When a person matures, the pace of cell multiplication slows. In adults, normal cells primarily multiply only to replace cells that die either due to exposure to a variety of external factors or naturally as a result of normal cellular wear and tear, which is related to the number of times the cell has multiplied.
When the processes that control the multiplication and life span of normal cells go awry, the cells start multiplying uncontrollably, fail to die when they should, and begin to accumulate. In body organs and tissues, these cancerous cells form a tumor mass, and in the blood or bone marrow, they crowd out the normal cells.
Without medical intervention, over time, some cancerous cells gain the ability to invade local tissues, and some spread, or metastasize, to distant sites. The progression of a cancer to metastatic disease is the cause of most cancer-related deaths.
Changes, or mutations, in the genetic material of the cells are the primary cause of cancer initiation and development. Not all mutations contribute to cancer development, but the greater the chance that a cell will acquire a mutation, the greater the chance that one of these mutations will cause cancer. The identity, order, and speed at which a cell acquires genetic mutations determine the length of time it takes for a cancer to develop and are influenced by numerous interrelated factors (see sidebar on Why Me? Why This Cancer?