SAN ANTONIO - Breast cancer experts are cheering what could be some of the biggest advances in more than a decade: two new medicines that significantly delay the time until women with very advanced cases get worse.

In a large international study, an experimental drug from Genentech called pertuzumab held cancer at bay for a median of 18 months when given with standard treatment, vs. 12 months for others given only the usual treatment. It also strongly appears to be improving survival; follow-up is continuing to see if it does.

"It's a spectacular result," said one study leader, Sandra Swain, medical director of Washington Hospital Center's cancer institute.

In a second study, another drug long used in organ transplants but not tried against breast cancer - everolimus, sold as Afinitor by Novartis AG - kept cancer in check for a median of seven months in women whose disease was worsening despite treatment with hormone-blocking drugs. A comparison group that received only hormonal medicine had just a three-month delay in disease progression.

Afinitor works in a novel way, seems "unusually effective," and sets a new standard of care, said Peter Ravdin, breast cancer chief at UT Health Science Center in San Antonio, who has no role in the work. Most patients have tumors like those in this study - their growth is fueled by estrogen.

Results were released Wednesday at a conference and some were published online by the New England Journal of Medicine.

The drugs, which have not proved to be cures, will likely cost up to $10,000 a month.