FISH technology accurate in measuring the HER-2 receptor in human breast tumors

The debate on how to select patients who will respond best to costly drug treatments for aggressive breast cancer now favors fluorescence in situ hybridization (FISH) to measure the HER-2 receptor found in human breast tumors, according to a leading pathologist presenting at the Association for Molecular Pathology annual meeting.

Michael Press, M.D., Ph.D., pathologist and Harold E. Lee Chair in Cancer Research, Norris Comprehensive Cancer Center, University of Southern California, told a symposium audience that a growing body of research in recent years demonstrates that FISH technology is an accurate, reproducible and predictive diagnostic method for testing women with breast cancer who are candidates for drug treatments targeted to the HER-2 tumor receptor. The drugs are Herceptin® (trastuzumab) and lapatinib. His remarks were presented at a symposium sponsored by Abbott Molecular.

HER-2 is a tumor marker for aggressive disease and to measure response to targeted therapies. The protein is a molecular target for the two medications, which suppress the HER-2 signal transduction pathway. For patients with HER-2-positive tumors, both drugs are clearly associated with improved clinical outcomes in metastatic breast cancer, and Herceptin is approved for use as adjuvant therapy.

Earlier this year, Press co-authored an article published in the Journal of Clinical Oncology refuting guidelines developed by the American Society of Clinical Oncology and the College of American Pathologists that recommended immunohistochemistry (IHC) as the preferred diagnostic method for determining a breast-cancer patient's HER-2 status.

"Evaluation of HER-2 status should consider the costs of treatment as well as the potential benefits of therapy," Press said. "And the cost of the diagnostic test is minimal compared with the cost of the medications. More accurate assignment of patients to treatment more than offsets the costs of erroneously treating women whose breast cancers lack HER-2 amplification.

In addition, there is the human cost of failing to treat women whose breast cancers have HER-2 amplification."

"An issue with FISH for HER-2 testing is that up to 2 percent of breast cancers have FISH ratios at or near the cutoff level. However, we are aware of no published data demonstrating that patients with borderline HER-2 amplification respond less favorably to trastuzumab and lapatinib," he said.