Cancer occurs as a result of mutations in genes that control cell growth and death. These mutations can be inherited or acquired, although inheriting a cancer susceptibility gene does not mean that someone will develop cancer. Only a small fraction of cancer cases have an inherited link. The notion that there is a particular gene that could make people more prone to suicide is controversial but there have been scientific studies that have genetically linked depression within families. However, there has been difficulty in proving that this is entirely separate from the environmental factors of dealing with bereavement from a relative lost to suicide. There have been notable cases of suicide appearing to run in families. In 2009, the son of Sylvia Plath and Ted Hughes, Nicholas, committed suicide over 45 years after his mother took her own life. Ernest Hemingway killed himself, as did his father, two of his siblings and his granddaughter. Incidentally, a 'suicide gene' in genetics causes a cell to kill itself (through a process known as apoptosis) and is a potential means of treating cancer.