Scientists were able to change living tissue in an animal to its embryonic state, which could be used to heal the body, BBC News reported.

Despite their success in turning the cells back to their embryo state, the scientist found in their study, published Wednesday in the journal Nature, that it only caused tumors to form in the test mice.

When an egg is fertilized, it has the potential to develop into every kind of cell in the body. When it develops, that transformability is lost, so being able to turn an adult cell back into an embryo has major healing potential and could regenerate a weak heart, brain or skin.

"It is a surprising result, this was not expected, most of us thought that it would be impossible," lead researcher Manuel Serrano told the BBC.

Researchers at the Spanish National Cancer Center said they have achieved the feat for the first time with an animal. It has been done before in laboratories by treating skin samples with a mix of chemicals.

Genetically modified test mice were given a drug meant to activate the production of chemicals that reverse the production of cells. Although the tissues successfully reverted to embryonic state, without further direction, the cells just turned into tumors.

"Of course this is not what we want for regenerative medicine," Serrano said. "We want to turn back the clock in a controlled manner and this is something we have to work out in the future."

Stem cell experts praised the research, but said much more needs to be done before leading to actual therapies.

"This is a really elegant study with important implications for the field," said Robin Ali, from the Institute of Ophthalmology in London, who is using stem cell technology to rebuild the retina to restore sight. "It will be a monumental task to prove this is safe, as what you're doing is innately dangerous, but it is exciting as it's potentially a new strategy for regenerative medicine."

Chris Mason, a stem cell scientists at the University College London, said the technique in the study would be favorable to stem cells.

"Overall it's very cool and potentially very exciting, but it has massive issues in terms of control," he said. "It's like a tree, instead of going down from a branch to the root and back up to a different branch, maybe we'll be able to jump from branch to branch."