There are some genes which help protect humans from developing cancer. Examples of these genes are: APC, MLH1, MSH2, MSH6, STK11, or BRCA. These genes, and others like them, are located on the autosomes. This means that an inherited predisposition for cancer can come from either your mother or your father, because you have one gene from each.
Some people are born with an alteration (mutation) in one of these genes. A mutation is essentially a mis-spelling of the gene. Mutations prevent genes from performing their jobs, which means proteins the body needs may not be made, or if they are made they may be formed incorrectly. Usually, people will only have a mutation in one copy of the gene. This means that they still have one working copy of the gene. However, this single copy of the gene is not able to make up for the mutated copy. Over time, the working copy of the gene also acquires mutations, which are random and happen by chance as people age; these types of mutations, which are acquired after birth, are not inherited. An individual who has an inherited mutated copy of a gene plus a randomly mutated copy of the same gene is more likely to develop cancer than someone who started life with two working copies of the gene.
If an individual has an inherited mutated copy of a gene, there is a 50% risk of passing the altered gene on to his or her children. The other 50% of the time, the working copy of the gene will be passed on to his or her children. Each child has a 50% risk of receiving the mutated gene.