Scientists in Oregon say they've reached the long-sought goal of cloning monkey embryos and extracting stem cells from them

it offers fresh hope in field that has been marked by frustration and even fraud. The claim of a similar breakthrough with human embryos by a South Korean scientist in 2004 turned out to be false.

one day, such a procedure could be used to create transplant tissue that's genetically matched to an ailing patient.

Scientists have tried for years to clone monkey embryos and extract stem cells because monkeys are more closely related to humans than other lab animals are.