"The FDA has concerns adipose-derived stem cells are a drug," he said, meaning they would need approval before trials could begin here.
"In the United States, this is a huge leap because these patients have breast cancer and we're still a little unsettled about the use of adipose-derived stem cells. We don't have a whole lot of good data."
So while researchers in the new trials may believe their treatments are a few years off, it may be some time before the U.S. would approve trials.
"We're probably a few years away from the FDA making that decision about adipose-derived stem cells," said Carlson.
He noted, however, that one red flag in the current trials was that animal data they were relying on did not appear to be in the medical literature.
One other researcher contacted by ABCNews.com declined to comment on the record because of a lack of peer-reviewed data, and pointed to two papers by the group running the Australian stem cell trial -- one at the Bernard O'Brien Institute of Microsurgery in Melbourne -- that had been retracted from their journals. ABCNews.com found at least one additional retracted paper by the group since 2005.
As of press time, professor Wayne Morrison, the head of the group, had not responded to a request from ABCNews.com for comment.
Dr. Peter Rubin, a plastic surgeon at the University of Pittsburgh, received a three-year grant from the National Cancer institute in 2006 to explore using adipose stem cells to regenerate lost tissue, and has since had that grant extended through 2012.
"This is a technology that's been rapidly evolving. I'm not surprised that we're getting to that point," he said of the British and Australian trials to regrow breast tissue. "I'm hoping that we're going to see promising results from this."
While he acknowledged that some women may prefer the speed of an implant, he noted that long-term, breast regeneration may have advantages.
"Long-term, that is going to have a better look and feel than an artificial implant reconstruction, and it will have less problems as well," said Rubin.
Tumor growth caused by stem cells may also be an issue, he acknowledged, but a lack of cell growth is one more frequently encountered by researchers.
"The bigger problem is that we have trouble getting the tissues to grow and maintain their shape and volume," said Rubin.
Ultimately, he said, we should be able to regenerate tissue with stem cells. What is less clear is whether that will come from the current trials.
"There's such a broad body of literature about fat stem cells and the ability of those cells…to play a positive role in regenerative medicine applications," he said of the retractions issued by the Morrison Group. "They're not the only people doing that stuff."
"I believe this is a promising field," Rubin said. "Whether or not that strategy is the right one, we will find out."