Evaluation of Genetic Status of HER-2/neu and Aneusomy 17 by Fluorescence In Situ Hybridization and Comparison with Immunohistochemistry Assay from Indian Breast Cancer Patients

Aims: The HER-2/neu proto-oncogene is amplified in 15%-25% of breast cancers. In the current study, we evaluated HER-2/neu status of 396 cases of breast cancer by fluorescence in situ hybridization (FISH), and the results were correlated with immunohistochemistry (IHC) for HER-2/neu protein expression. Results: Overall, HER-2/neu amplification was observed in 38.4% of cases. Concordance between IHC and FISH was 90.4% considering only IHC score 0, 1 (negative), and 3 (positive). However, only 37.3% of the IHC score 2 (equivocal) cases showed HER-2/neu gene amplification. A majority of the discordant cases within the IHC negative (score 0 and 1) and IHC positive (score 3) were high-grade tumors. Polysomy 17 and monosomy 17 was seen in 7.3% of the total cases of each. Furthermore, a majority of FISH positive cases were noted in Intraductal Carcinoma grade III and cases with regional lymph nodal metastasis. Polysomy 17 was seen in 7.9% of the FISH positive cases and in 6.3% of the FISH negative cases. Monosomy 17, however was more preponderant in FISH negative cases. Conclusion: We believe that the FISH test should be considered as the gold standard in the estimation of the HER2/neu status due to its increased sensitivity and better appreciation of aneusomy 17.