An experimental breast cancer drug made from sea sponges added months to the lives of breast cancer patients whose cancer had come back despite several rounds of chemotherapy, doctors reported Sunday.

Eisai's eribulin added an average of two and a half months to the lives of patients dying of breast cancer, which is a big improvement in such seriously ill cancer patients, the international team of researchers said.

The results of the Phase III trial, presented to a meeting of the American Society of Clinical Oncology in Chicago, have been anticipated after Eisai was given priority review June 1 for U.S. Food and Drug Administration approval of the drug.

"This is potentially practice changing," ASCO president Dr. Douglas Blayney said in a telephone interview.

Dr. Christopher Twelves of St. James Hospital in Leeds in Britain and an international team studied 762 breast cancer patients with different types of tumor.

All had cancer that had spread and been through at least two rounds of chemotherapy. Two-thirds got two doses of eribulin while getting standard treatment, usually with one other chemotherapy drug but occasionally with just supportive care to treat pain and other symptoms.

The other third got either a third round of chemotherapy or supportive care. "Once this treatment fails, the patient often died," Blayney said.

The patients given eribulin did considerably better, the researchers told the meeting. The eribulin patients lived a median of 13 months, compared to just under 11 months for patients who did not get eribulin.

LONGER LIVES

Most cancer trials look for what is called progression-free survival, meaning the doctors are looking to see if the tumors start growing back, or sometimes just response rate, to see if the tumors shrink at all.

This one looked to see how long the patients actually lived.

"This study is the first to compare overall survival with this new chemotherapeutic agent to real-life choices in heavily pretreated patients with metastatic breast cancer," Twelves and colleagues said in their written presentation.

The drug works on the same principle, but with a slightly different mechanism, as older cancer drugs called taxanes and is infused intravenously.

Other experts said eribulin could be one of the last new chemotherapy drugs, which typically target fast-growing cells that include tumors but also healthy cells.

"This is the era of targeted therapy. It's not an era of chemotherapy," said Dr. Eric Winer of Harvard's Dana-Farber Cancer Institute in Boston, who was not involved in the study.

"I don't know that there are going to be many more chemotherapy agents approved for women with breast cancer. That said, this may be one of the last, and potentially provide women with an additional option and maybe an option to be used in combination with targeted therapies in the future."

Three other studies presented to the meeting showed eribulin was effective and tolerated in a different group of patients with breast cancer, as well as colon cancer and urinary cancer patients.

Eisai has filed in Japan, the United States and Europe for approval of eribulin. The company hopes it will become a blockbuster, with global earnings of $1 billion a year.

"I think there is a reasonable chance that this drug will actually get approved," Winer said. "There aren't many drugs that show a survival advantage in this setting."