Discrepancies in Clinical Laboratory Testing of Eligibility for Trastuzumab Therapy: Apparent Immunohistochemical False-Positives Do Not Get the Message

Abstract

Discordant HercepTest/FISH results, and to a lesser extent discordance with CB11 IMH, are most commonly false-positive results with a score of 2+. The 2+ score as defined in the guidelines for the FDA-approved HercepTest should not be used as a criterion for trastuzumab therapy unless confirmed by FISH. Determination of Her-2 gene copy number by FISH may be a more accurate and reliable method for selecting patients eligible for trastuzumab therapy.