Scientists at the University of Texas M. D. Anderson Cancer Center have identified a microRNA (miRNA) that could potentially separate the patients who will respond to Herceptin from those who will not.

Herceptin was approved to treat HER2 positive breast cancer in 1998 and is considered by many to be a revolutionary therapy. However, only about 35 percent of patients who receive Herceptin as a single agent will respond to the therapy, according to data presented at the American Association for Cancer Research 101st Annual Meeting 2010.

"If we know in advance who is going to respond to treatment, then this could possibly save patients from undergoing this treatment unnecessarily," said Sumaiyah K. Rehman, a third-year graduate student in the lab of Dihua Yu, M.D., Ph.D., Hubert L. and Olive Stringer distinguished chair in basic science, professor and deputy chair of the department of molecular and cellular oncology and director of the cancer biology programme at the University of Texas M. D. Anderson Cancer Center.

Herceptin has been linked with heart problems in 2 percent to 7 percent of cases, and patients often have to weigh the risk of heart disorders against the risk of their continuing cancer.

In the current study, scientists found that breast cancer cells with increased miR-21 and reduced PTEN expression were significantly more resistant to Herceptin than control cells. PTEN loss had been previously linked to Herceptin resistance in another study published from the same group and confirmed by other research groups.

The scientists further tested this finding in patients and found that high levels of miR-21 were significantly correlated with poor response to Herceptin. Rehman said she would continue her study to better understand the mechanisms of miR-21-mediated resistance.

"MiRNAs have been reported to control up to 35 percent of our genome, so there are many discoveries remaining," said Rehman. "This is one drop of information in the bucket of knowledge that is hardly full in what we can learn."

Source: The American Association for Cancer Research