The oncogenesis process is caused by these mutations in the genetic material of normal cells, which alter the normal balance between proliferation and cell death. As a result there is an uncontrolled cell division and an evolutionary process of these cells through natural selection within the organism. Rapid and uncontrolled reproduction of cells can produce benign tumors and some types of these tumors can become malignant, which is what is known as cancer. Benign tumors do not spread to distant parts of the body or invade other tissues, and usually do not pose a threat to life unless they compress vital structures or have some physiological activity (for example, that they are capable of producing a hormone) . Malignant tumors are able to invade other organs, spread to distant places (a process known as metastasis) and become a threat to life.