* Up to two thirds of patients not tested for HER2
* Study suggests drug may be misused in clinical practice
LONDON, Sept 14 (Reuters) - A genetic test to determine if women should receive Roche's ROG.VX breast cancer drug is frequently not given, U.S. researchers said on Monday.
Up to two thirds of patients with aggressive breast cancer had no documentation of the test in their health insurance records, according to a study published online by the journal Cancer.
The research also found that one in five genetic test results may be incorrect.
Herceptin, a blockbuster product for Roche, can save lives. But it only works for about 20 percent of women whose tumours overproduce a protein called HER2, and identifying these HER2-positive patients requires a genetic test.
The researchers said their findings suggested many breast cancer patients who might benefit from Herceptin, also known as trastuzumab, were not receiving it, while some women on the drug had never been properly tested.
"Our review of the literature suggests that there are important knowledge gaps regarding the real world use of HER2 testing and trastuzumab," Elena Elkin, a researcher at Memorial Sloan-Kettering Cancer Center in New York and one of the study's authors, said in a statement.
"Filling these gaps may help optimise limited healthcare resources and improve care for women with breast cancer."
GlaxoSmithKline (GSK.L) also has a newer medicine for HER2-positive breast cancer called Tykerb. (Reporting by Ben Hirschler, Editing by Lin Noueihed)