Certain changes in our DNA sequence lead to the disorder we know as cancer. Therefore, cancer is not contagious. The defects that cause cancerous growth of cells are accumulated over time. Cancer cells divide at inappropriate times. These cells either do not receive signals to stop dividing, or they may not require outside signals to start dividing.
Cancer cells lose their normal awareness of their position with respect to other cells.
When cancer cells encounter neighbors, they do not stop dividing as normal cells do, but pile up and form a tumor. The genes that control the processes listed above for normal cells are the genes that are mutant in cancerous cells. Genes mutant in cancerous cells include those whose normal function is to prevent cell division, to help cells sense their environment and respond properly to it, and to help cells in their normal process of adhering to other cells. Understanding the normal situation as well as the cancerous state will lead to better methods of prevention and treatment. Mitochondrial Disorders These relatively rare disorders are caused by mutations in non-chromosomal DNA located within subcellular organelles, the mitochondria.