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."
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 tumour growth," she said.
The breakthrough, reported today 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.
The more immediate motivation for the work is in understanding how breast cancer develops. "There's a growing idea that cancers originate in cells that must have the ability to divide many times in order to accumulate many mutations," said Dr Eaves. It is this chain of mutations that makes them divide uncontrollably.
But most cells in a tumour are not destined to continue dividing indefinitely, so successful therapy needs to remove the cells that are."Only a subset of cells in the tumour can keep regenerating - they are the cancerous equivalent of the natural stem cell," said Dr Eaves.
By understanding the stem cells better, the teams hope to get a better handle on the cells at the heart of a tumour.
"The real impact of our findings is in providing a new basis for understanding the cell which gives rise to breast cancer - and the possibility of developing drugs that target this cell," said Dr Visvader.