Chasing the immortal strand: evidence for nature's way of protecting the breast genome

Mutations arise during cell division at a predictable rate. Besides DNA repair mechanisms, the existence of cellular hierarchies that originate with a stem cell serve to reduce the number of divisions necessary for normal physiology. In a previous issue, Bussard and colleagues demonstrate that mammary stem cells have an additional remarkable trait; namely the ability to selectively retain a template DNA strand during self renewal. In doing so, they avoid the accumulation of mutations in that so called 'immortal strand'. The implications of this are discussed with reference to the development and treatment of cancer.