The study focussed on breast cancers that are fuelled by estrogen-these are called estrogen-receptor or progesterone-receptor positive cancers (ER or PR positive).
Women who have ER or PR positive metastatic breast cancer often take anti-hormonal medicines, such as aromatase inhibitors to slow down cancer progression, however, cancer becomes resistant to this approach and begins to grow.
"At first, the tumour's growth is halted because the aromatase inhibitor is depriving the cancer of the estrogen it needs to grow," said Claudine Isaacs, M.D., clinical director of breast cancer program at Georgetown University Medical Centre's Lombardi Comprehensive Cancer Centre.
"Eventually, though, the cancer will figure out another way to thrive in the absence of the estrogen," she added.
The research team led Isaacs including Indian origin lead author Deepa Subramaniam, M.D. of Lombardi, are conducting a clinical trial to see if a new approach can destroy the machinery the tumour creates in order to grow without the estrogen. The drug being studied is called sorafenib.
The preliminary results have shown clinical benefit response in 26 percent of the patients taking both sorafenib and anastrozole.
"Given what we know about the ineffectiveness of sorafenib alone in metastatic breast cancer, we believe the benefit that we're seeing may be attributable to the restoration of sensitivity to aromatase inhibitors," said Isaacs.
"To manage breast cancer long term, it's apparent that we may need to continually switch drugs to keep up with how a cancer evolves and evades each approach. In a sense, for each step back, we hope to take two steps forward," she added.
The study was presented at the ASCO 2008 Breast Cancer Symposium.