Two teams of scientists have grown replacement breasts in mice, the first time an entire organ has been grown from scratch artificially.
The researchers say if the feat can be repeated in humans, it might one day allow women who have had a mastectomy to regrow their breast.
"That's not a dumb idea," said Connie Eaves at the University of British Columbia in Vancouver, the leader of one of the studies.
She said starting from scratch with a new breast might be easier than trying to intervene when things have gone wrong.
"We might be able to do that way before we can cure breast cancer," she said.
Jane Visvader of the Walter and Eliza Hall Institute of Medical Research in Parkville, Australia, who led the second team, was more cautious. "The same conditions that promote breast regrowth could possibly also promote breast tumor growth," she said.
The breakthrough, reported yesterday in the journal Nature, was to identify the stem cell type that gives rise to breast tissue.
By injecting one of these into a structure called the mammary fat pad, the teams showed that just one stem cell could grow into a breast in five weeks, the normal development time in mice.
One of the teams also showed that the reconstituted breasts could express milk.
Scientists have been able to reconstitute bone marrow from stem cells in the past, but this is the first time they have regrown a discrete organ.