Cancer is a disease both caused by genetics and environmental factors. Each person has either proto-oncogenes or oncogenes. These are the genes that are responsible for regulating cell division. When a person has an oncogene it is a mutation of a proto-oncogene.
The oncogene (dominant gene) tells the cell to continuously divide. This can be a problem if the cell is cancerous. Cancer cells are caused by a mutation in DNA. When the body is exposed to cancer causing factors known as carcinogens there is a higher probability of cancer. Carcinogens randomly destroy and mutate parts of DNA.
They only become a problem when they mutate a part of DNA affecting that area of the body, so when the cell divides its when it transforms. People with oncogenes are more predisposed to cancer because there is no signal to make proteins to inhibit the cell form dividing. Luckily there is a gene know as tumor suppressor genes. These genes code for proteins that stop the cell division.
There are also caretaker genes that code for enzymes to fix the problems in replicated DNA. So for someone who has oncogenes the body has other genes that act as a back up to prevent the division on cancerous cells. There are many environmental factors that contribute to cancer but genetics also determines a person’s probability of cancer spreading. No matter how healthy and environment or how good your genes are everyone is still at a risk of getting cancer because all it takes is the replication of one mutated gene.