There has been considerable interest in the genetic causes of cancer for many years now. The theory here is that if we understand which genes are responsible for uncontrolled cell division, then it might be possible to treat the cancerous cells. In addition, there is the notion that many cancers are genetically inherited and that the disease is therefore a problem of heredity.
However a landmark study of 90,000 Swedish twins showed that the environment is the main cause of cancer in that if a twin got cancer the other did not necessarily get it, showing that environmental factors are mainly to blame.
It is also known that a relatively small percent of breast cancers are inherited. Breast cancer is a relatively uncommon disease in Asian women but when they adopt Western habits the incidence starts to rise thereby indicating that it is something external to them that is causing the disease.