The first medicine produced from a genetically modified animal has been recommended for use in Europe.
The goat produces a human anti-clotting protein in its milk
The European Medicines Agency (EMEA) has reversed an earlier decision not to issue a licence for the drug, ATryn, after taking further expert advice.
The drug is extracted from the milk of goats engineered to carry a human gene involved in inhibiting blood clots.
ATryn will be used during surgery on patients with a rare condition that makes their blood clot too easily.
About one person in every 3,000-5,000 is in this position.
They are born missing a copy of the gene that makes a protein called anti-thrombin, an anticoagulant - a substance that prevents coagulation of the blood.
Normally, vulnerable patients are maintained on blood thinners such as Warfarin but if they are giving birth or undergoing surgery this is deemed too risky, and they are given replacement anti-thrombin.
Currently, anti-thrombin is extracted from human blood plasma; but fears about the possible transmission of disease, such as vCJD, make doctors unwilling to expose their patients to plasma products unless they have no choice.
The US-based company GTC Biotherapeutics set out to address this problem by producing a human version of anti-thrombin in animals.
Risks vs benefits
They genetically modified goats to contain the human gene that codes for anti-thrombin. The transgenic animals produce the protein in their milk.
The EMEA turned down in February this year the company's original application to market the drug processed from the milk.
It said the company had not presented enough scientific evidence that the medicine's benefits outweighed its risks.
But after re-examining the application data and meeting with experts, the EMEA has now given the drug the go-ahead for use in Europe, subject to final approval later this year.
Tom Newberry of GTC Biotherapeutics said the approach of using transgenic animals would lead to lower development costs and a broader range of treatments for patients.
GTC claims one goat produces the equivalent of 90,000 blood collections.
"This is a technology which has the potential to dramatically change the way in which expensive biological drugs are developed for the commercial marketplace," he told the BBC News website.
In a statement on the company's website, Professor Isobel Walker, consultant haematologist at the Glasgow Royal Infirmary, UK, said: "It is a good day for European patients with congenital anti-thrombin deficiency and for their physicians."