Have you ever heard about a rare form of cancer or other unusual disease and asked whether it was "genetic"? Chances are, you were really wondering if it was passed down from a parent (inherited), as opposed to occurring out of the blue.
The word genetic simply means "of or relating to the genes" [source: Merriam-Webster]. All cancers are in fact genetic, in that they develop as a result of gene mutations, but only 5 to 10 percent are hereditary, or caused by genetic changes passed down from one generation to the next [source: Staten Island University Hospital]. Most of the rest -- 70-80 percent -- are known as sporadic cancers and are the result of genetic changes that occur during our lifetimes.