New drug may target hard-to-treat breast tumours

By Michael Kahn

LONDON, Feb 23 (Reuters) - An experimental drug that makes cancer cells susceptible to a widely used treatment could help women with a hard-to-treat and often more aggressive form of breast cancer, researchers said on Monday.

About a third of women develop so-called estrogen-negative tumours, which means their cancer does not respond to tamoxifen, said Caroline Ford and colleagues at Lund University in Sweden.

But their new drug called Foxy-5 activates the estrogen receptor -- a kind of molecular doorway on cells that allows tamoxifen to work, they reported in the Proceedings of the National Academy of Sciences.

"It flips the switch basically," Ford said in a telephone interview. "It makes breast cancer cells respond to tamoxifen in women who cannot be treated with the drug," she added. "If you don't have that molecule you can't get tamoxifen because there is no target."

Breast cancer is the leading cause of cancer deaths among women worldwide, according to the American Cancer Society. The group estimates about 465,000 women died of breast cancer globally in 2007, and 1.3 million new cases were diagnosed.

Tamoxifen has been shown to reduce the risk that breast cancer will return after surgery, at least among patients with so-called estrogen-receptor-positive cancer, the most common type. It works by blocking estrogen from causing wild cell growth.

The study of cancer cells in a lab shows the experimental drug may one day offer better options for the third of women who develop estrogen-receptor-negative tumours.

The treatment is not an alternative for a new class of drugs called aromatase inhibitors such as AstraZeneca's (AZN.L) Arimidex, Ford said.