The complicated bases of these diseases make them difficult to study and to treat. Heart disorder, diabetes and cancer are examples of this type of disorder. 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.