Assessment of c-erbB2 Expression by IHC and FISH in Invasive Breast Cancer— A Comparative Study: Experience from a Single Institute

Introduction: An accurate assessment of c-erbB2 expression in invasive breast cancer (IBC) has become crucial to precisely recognize the candidates to be treated with Trastuzumab. Presently, fluorescence in situ hybridization (FISH) and immunohistochemistry (IHC) are most commonly employed methods for evaluating c-erbB2 status. Recent literature has documented a strong correlation between the two c-erbB2 diagnostic analyzes. However, discordance between both the assays has been rarely reported. Therefore, we aimed to compare and correlate FISH and IHC results for c-erbB2 expression in Indian breast cancer patients. Material and methods: A total of 388 formalin fixed, paraffin embedded blocks of invasive breast cancer were retrospectively evaluated for c-erbB2 status by IHC (DAKO) and FISH (PathVysion dual-probe system) and results were compared. Results: 92.5% cases with IHC 3+ score showed significant concordance with the FISH results; while c-erbB2 gene amplification was noted in 48.3% of IHC 2+ cases. A large number of referral cases in the study group and variation in pre-analytical and analytical factors have attributed in escalating the number of indeterminate cases expressing c-erbB2 gene amplification. Additionally, an inverse correlation was revealed between ER/PR expression and c-erbB2 status. Conclusion: The results of the current study established a high degree of concordance between IHC and FISH in Indian breast cancer patients with 3+ immunoreactivity. However, reflex testing by FISH is recommended for IHC equivocal cases in order to avoid false results related to technical and interpretation errors, usually encountered while performing an immunohistochemical assessment.