IntroductionBefore any new methodology can be introduced into the routine diagnostic setting it must be technically validated against the established standards. To this end, a ring study involving five international pathology laboratories was initiated to validate chromogenic in situ hybridisation (CISHTM) against fluorescence in situ hybridisation (FISH) and immunohistochemistry (IHC) as a test for assessing human epidermal growth factor receptor-2 (HER2) status in breast cancer.
Methods:
Each laboratory performed CISHTM, FISH and IHC on its own samples. Unstained sections from each case were also sent to another participating laboratory for blinded retesting by CISHTM (’outside CISHTM’).
Results:
A total of 211 invasive breast carcinoma cases were tested. In 76 cases with high amplification (HER2/CEP17 ratio >4.0) by FISH, 73 cases (96%) scored positive (scores [greater than or equal to] 6) by ‘outside CISHTM’. For FISH-negative cases (HER2/CEP17 ratio