Genetic Alterations in HER2-Positive and Equivocal Breast Cancer by Immunohistochemistry.

PURPOSE

We aimed to identify genetic alterations in groups with different HER2 immunohistochemical (IHC) scores.

PATIENTS AND METHODS

A total of 120 patients with HER2-positive breast cancers, including 89 cases with IHC 3+ tumors and 31 cases with IHC 2+ and positive for in situ hybridization (ISH) were enrolled. Molecular profiles were determined using Thermo Fisher TMO comprehensive assay on surgically removed tissues. All called variants were compared between IHC3+ and IHC2+/ISH+ groups by Fisher exact test.

RESULTS

There was a significantly higher sample frequency 94.4% (84/89) of amplification in IHC3+ group than that in IHC2+/ISH+ group 45.2% (14/31). By contrast, there was a significantly lower sample frequency of _AMP_CNA 10.1% (9/89) and _AMP_CNA 0% (0/89) in IHC3+ group than those in IHC2+/ISH+ group with sample frequency 25.8% (8/31), and 9.7% (3/31), respectively.

CONCLUSION

We conclude that HER2 IHC3+ tumors have higher frequency of _ AMP_CNA and lower frequency of _ AMP_CNA and _AMP_CNA than IHC2+/ISH+ tumors. These results provide therapeutic strategies in treatment of HER2-positive breast cancer.