The study, published in the journal Clinical Cancer Research, found the oral chemotherapy drug lapatinib benefits women with HER2-positive breast cancer, while women with HER2-negative breast cancer, or those who express EGRF alone, derive no incremental benefit.

In addition, a misclassification of metastatic breast cancer patients by as much as 10 percent prevents some people from receiving optimal therapy.

The lead author, Dr. Michael Press of the Norris Comprehensive Cancer Center in Los Angeles, said women with HER2-positive metastatic breast cancer who receive lapatinib and chemotherapy have shown an improvement of about 50 percent in progression-free survival when compared with chemotherapy alone.

Unfortunately, high-volume laboratories using laboratory technicians instead of pathologists to score gene amplification misclassify about 10 percent of HER2 amplified breast cancers as not amplified, preventing these patients from being candidates for lapatinib, Press said.

"I would like to see all women with breast cancer tested appropriately, using the best method and certified personnel, to assess the HER2 status of their breast cancer so the appropriate treatment can be selected," Press said in a statement.