NEW YORK (Reuters Health) - New clinical practice guidelines released this week focus on the accuracy of testing for human epidermal growth factor receptor 2 (HER2) in invasive breast cancer.

The American Society of Clinical Oncology (ASCO) and the College of American Pathologists (CAP) collaborated in developing the new recommendations, emphasizing that accurate measurement of the HER2 gene or its expression is central in determining therapy for patients with invasive breast cancer.

The new guidelines are needed, the panel notes, because previous guidelines were developed prior to completion of trastuzumab (Herceptin) clinical trials, an agent effective in many patients with invasive breast cancer that overexpresses HER2. Older recommendations also failed to include methodology, quality control, or associations with clinical outcome.

Co-lead authors, Dr. Antonio C. Wolff, from Johns Hopkins University, and Dr. M. Elizabeth H. Hammond, from the University of Utah, and their associates emphasize that testing should be performed only on the invasive component of the breast cancer.

Rather than recommending only one test, the committee notes that testing using either immunohistochemistry (IHC) or fluorescence in situ hybridization (FISH) is acceptable, as long as accuracy is maintained.

In their report, published online and scheduled for joint publication in the January print issues of the Journal of Clinical Oncology and the Archives of Pathology and Laboratory Medicine, the panel presents two algorithms, depending on which assay is used.

They also summarize sources of HER2 testing variation, prior to, during, and after analysis; sample exclusion criteria, IHC and FISH interpretation criteria, and reporting elements for both evaluations.

"The panel strongly recommends validation of laboratory assay or modifications, use of standardized operating procedures, and compliance with new testing criteria to be monitored," Drs. Wolff and Hammond and their group write. They urge the use of stringent laboratory accreditation standards, proficiency testing, and competency assessment.

Adherence to the guidelines is voluntary, the investigators add, and physicians should continue to make their treatment decisions in light of each patient's individual circumstances. However, the College of American Pathologists will require all laboratories that it accredits to complete HER-2 testing proficiency training.

The authors also discuss the quandary that physicians face regarding equivocal results or when IHC and FISH test results are discordant. They point out that these patients will require further testing, and they advise that principal investigators evaluating this subgroup pool their outcome data to permit joint analysis of small trials.

J Clin Oncol 2007;25.