The fight against breast cancer, the second most dangerous after lung cancer, is making progress, but has experienced a number of setbacks, scientists said.

The most interesting progress was reported in a new study unveiled here Sunday that found that a new agent derived from a marine sponge can extend the survival rates of women with locally recurrent or metastatic breast cancer who already received extensive standard therapy.

The synthetic component called eribulin mesylate mimics a component found naturally in sponges and can prevent cell division, which causes cells to self-destruct, said study authors who presented their findings at the annual American Society of Clinical Oncology conference here.

In a randomized international trial, British researchers assessed the survival rates of 762 patients, treated either with eribulin or another therapy, almost always chemotherapy, and found the new therapy extended median overall survival by about 2.5 months.

"Until now, there hasn't been a standard treatment for women with such advanced breast cancer. For those who have already received all of the recognized treatments, these are promising results," said lead study author Christopher Twelves.

"These findings may establish eribulin as a new, effective option for women with heavily pre-treated metastatic breast cancer," said Twelves, head of the Clinical Cancer Research Groups at the Leeds Institute of Molecular Medicine in Britain.

The most frequently reported adverse effects among patients treated with eribulin were fatigue (53.7 percent), low white blood cell counts (51.7 percent), hair loss (44.5 percent) and numbness and tingling in different parts of the body (34.6 percent).

Serious adverse effects were reported for 25 percent of patients, the researchers said.

More than one million women a year are diagnosed with breast cancer worldwide, according to international statistics.

Approximately 50 percent of them are expected to develop recurrent or metastatic disease within 15 years of their first diagnosis.

Only one in five women with metastatic breast cancer survives longer than five years.

In the United States, an estimated 155,000 women are currently living with metastatic breast cancer, and that number is projected to increase to 162,000 by 2011.

"Women with advanced breast cancer are in critical need of new treatment options," said Alton Kremer, head of clinical development for oncology at Eisai Inc., the developer of eribulin

"In this study, eribulin has shown an improvement in survival, and if approved by health authorities, it may offer patients a new treatment option at this stage of the disease," he added

An application for marketing the drug was granted priority review status by the US Food and Drug Administration last month.

Another study presented at the conference showed that partial targeted irradiation of affected breasts can be effective. But some researchers reported setbacks.

A study by the John Wayne Cancer Institute in Santa Monica, Calififornia has concluded that removing additional underarm lymph nodes to look for more breast cancer cells in women with limited disease spread does not improve survival.

An observational trial of more than 5,500 women with early-stage breast cancer who had breastsparing surgery showed that using immunohistochemistry to detect hidden micrometastases in sentinel lymph nodes and bone marrow does not predict overall survival and should not be used to guide treatment decisions.

Yet another report found that shows that the characteristics of tumors in women with metastatic breast cancer often change when cancer spreads to the liver, requiring a change in therapy in more than 12 percent of patients.