Cancer is the term given to a group of diseases caused by an uncontrollable growth and spread of abnormal cells. Cancer cells, also referred to as malignant cells, are cells that have been genetically altered to look and function differently from normal cells. Thus, cancer is actually a disease of the cells and involves a series of mutations or changes in the genetic makeup, or DNA, in the cell.
Normal cells in the body usually divide when the body needs more cells. When signaling for new cells, the body is careful that it only triggers cells to divide when it needs more so that cell birth equals cell death.
Proto-oncogenes, cells that promote cell division, and tumor suppressor genes, which keep cell division in check, are in place to control cell division in an organized way.
In most cancers, the cells undergo at least four mutations, and in many cancers, mutations occur in both the proto-oncogene, making it an oncogene, as well as the tumor suppressor gene, so that there is no longer any control of cell division.
Cancer cells differ from normal cells in a number of ways. Cancer cells have uncontrolled, often rapid, growth rates. Generally, they are not encapsulated, so that the shape of the tumor is irregular, often with finger-like projections that invade neighboring tissue. They also have an abnormal structure, which often is poorly differentiated and has the ability to migrate or spread.
Metastases, or spread of tumor cells beyond the primary mass, can occur in three specific ways: