MELBOURNE, AUSTRALIA - JANUARY 5: This undated handout photo supplied by The Walter and Eliza Hall Institute of Medical Research on January 5, 2006 in Melbourne, Australia shows a branching network of milk transport ducts, typical of development within the mammary gland which were derived from a single stem cell. Researchers at the institute discovered the rare breast stem cells which could lead to new drugs or therapies to treat breast cancer. A subset of breast cancers may arise from a faulty stem cell or from other faulty cells produced by the stem cell. (Photo by The Walter and Eliza Hall Institute of Medical Research via Getty Images)
