A drug derived from sea sponges extends the life of women with an especially aggressive form of breast cancer by almost five months.
Two major trials involving more than 1,800 women with metastatic, or spreading, breast cancer found eribulin boosted survival by more than two months.
The most significant improvement was seen in women with the advanced triple negative breast cancer, a form of the disease with limited treatment options.
Eribulin increased the lifespan of these women by nearly five months. It also added more than two months to the lives of women with HER2 negative breast cancer, another hard-to-treat disease.
The drug was originally developed from a sea sponge called Halichondria okadai but is now made in laboratories.
Professor Chris Twelves from Britain's University of Leeds said the results were encouraging.
"Our results show a substantial improvement in survival for women with metastatic triple negative breast cancer, and a more modest, but significant, benefit for those with HER2 negative breast cancers.
Despite advances in the diagnosis and treatment of women with breast cancer, more than 11,600 women still die from invasive breast cancer each year in the UK.
"New and better treatments are needed for people fighting the disease," he said.
The findings were presented at the National Cancer Research Institute cancer conference in Liverpool.
Martin Ledwick, head information nurse at Cancer Research UK, said eribulin offered hope to those most in need.
"These results are encouraging and may offer valuable extra time to patients whose cancers have stopped responding to conventional treatments and have few options left.
"Advanced breast cancer can be very difficult to treat so these results take us a small, important step in the right direction.
"Although eribulin isn't a cure, it's an extra treatment option for patients with advanced breast cancer, which can be priceless to them and their families."
- PAA