Assessment of Human Epidermal Growth Factor Receptor 2 (HER2) Amplification by <i>In Situ</i> Hybridization (ISH): Findings from a Nationwide Program in Australia.
Authors: M. Bilous, G. Farshid
Journal: Cancer Research (2009)

Abstract Background: The HER2 gene is amplified in 18–20% of breast cancers. Trastuzumab (Herceptin®), an anti-HER2 monoclonal antibody, has survival benefits in HER2-positive breast cancer in both the metastatic and adjuvant settings. Evaluating HER2 status is, therefore, recommended in all primary breast cancers. The Australian In Situ Hybridization Program is the first nationwide program using ISH as the first-line testing platform. It was launched as a multicenter coordinated project to provide ISH testing for all primary breast cancers across Australia and to regulate HER2 testing.Methods: The following criteria were required for including a laboratory (lab) in the program: ≥50 ISH tests per pathologist, ≥150 per lab annually; training for pathologists and technicians; accreditation and certification of pathologists, technicians, and lab as per the Royal College of Pathologists of Australasia and National Association of Testing Authorities requirements; reporting time of 7 working days. A validated single-probe ISH test was used, with a chromosome 17 probe used for equivocal and possible polysomic cases. Cases that remained equivocal after dual-probe testing were tested by fluorescence ISH at a central lab. From March 2008, ISH scoring adhered to the 2007 ASCO/CAP recommendations. Only patients with ISH-positive primary tumors are eligible for adjuvant trastuzumab under the Australian government-funded Pharmaceutical Benefits Scheme.Results: 22 labs are approved for ISH testing: 10 use chromogenic ISH (CISH), 12 use silver ISH (SISH). Between October 2006 and September 2008, 20,406 ISH tests were reported: 8348 in the first 12 months (7835 primary, 513 metastatic) and 12,058 in the subsequent 12 months (11,594 primary, 464 metastatic). The HER2-positivity rate decreased in the second 12 months for primary (23.8% to 16.9%) but increased for metastatic (22.6% to 25.4%) cases. The number of core biopsies tested remained consistently low (3.7% and 4.5%), with testing performed primarily on excised tumor. Average ISH reporting time reduced slightly (4.9 to 4.7 days). Test repeat rates decreased for CISH labs (8.9% to 8.2%) but were higher for SISH labs (13.7%) because of a global issue of silver wash contamination that was subsequently addressed and resolved. Immunohistochemistry (IHC) was performed on 75% of samples and was used to allow evaluation of problematic or equivocal cases, or referrals from labs in the start-up phase of testing. Given this bias, the proportion of IHC 3+ samples amplified by ISH was relatively low but increased from 80.2% to 84.4% in the second 12 months.Discussion: The reduced HER2-positivity rate for primary cases, reporting times, and repeat rates (CISH labs only) reflects the increased number of ISH tests performed, increased lab experience, and improvements in testing accuracy. These data reflect the successful implementation of a regulated, nationwide testing program that continues to collect data on HER2 testing in patients with breast cancer. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 5100.