In these cases, the gene combination the individual inherited has an increased tendency to develop into a specific form of cancer. Some genetic effects are dominant, while others are recessive. Normal cells have two copies of each gene. Environmental factors include certain types of radiation, chemicals, and viruses. These factors usually directly mutate the DNA within the cell's nucleus.
Some chemicals can cause cancer.
The most prominent examples of carcinogenic chemicals are those found in tobacco smoke and asbestos used in insulation or as a fire retardant. When smoked or chewed, tobacco releases carcinogenic compounds into your body. Viruses may also play a role in cancer formation. However, only a few types of viruses are known at present to contribute to human cancer. In one case, the mutation is analagous to pushing down n the accelerator of an automobile, to speed up cell division.