Some tumours are heritable whereas others are not. Tumours are caused by mutations. In what type of cell would a mutation that resulted in a heritable tumour occur? Why are only some tumours heritable?

For a tumour to be passed from one generation to the next the tumour causing mutation must occur in a germ cell that is used to produce eggs or sperm. If the mutation occurs in a non-germ cell it cannot be passed to future generations. However, the mutation will be passed on to the cells that are formed by mitotic division of the mutation containing cell and as a result the number of mutation containing cells in the body will progressively increase. Mutations frequently occur during mitosis but they are generally corrected by DNA repair mechanisms in the cell. If people have inherited faulty DNA repair genes their risk of cancer will be increased, so an increased risk of any type of cancer can be hereditary.