Can breast cancer patients with HER2 dual-equivocal tumours be managed as HER2-negative disease?

BACKGROUND: Increasing human epidermal growth factor receptor 2 (HER2) immunohistochemistry (IHC)/fluorescence in situ hybridisation (FISH) dual-equivocal breast tumours are reported after the 2013 American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP) guideline update. The aim of this study is to investigate the clinico-pathologic characteristics, treatment patterns and disease outcome of these patients with HER2 dual-equivocal tumours.

PATIENTS AND METHODS: Patients with HER2 IHC 2+ and available FISH results were retrospectively analysed from the Comprehensive Breast Health Center, Shanghai Ruijin Hospital. The 2013 ASCO/CAP guideline was applied to define HER2-positive, dual-equivocal and -negative groups. Patient characteristics, systemic treatment patterns and survival were compared among these groups. Reverse transcriptase-polymerase chain reaction-based assays were applied to test HER2 mRNA expression level.

RESULTS: Among 691 patients included, 133 (19.25%) were HER2 positive, 25 (3.62%) were HER2 dual-equivocal and 533 (77.13%) were HER2 negative. Univariate and multivariate analyses stated that HER2 dual-equivocal tumours shared more similarity with HER2-negative tumours, whereas HER2-positive tumours had rather different clinico-pathologic features. HER2 dual-equivocal tumours had similar HER2 mRNA levels compared with HER2-negative tumours (P = 0.26), which were much less compared with HER2-positive breast cancer. Besides, adjuvant systemic treatment patterns were comparable between HER2-negative and dual-equivocal tumours, and none of HER2 dual-equivocal patients received anti-HER2 treatment. There was no survival difference among these three groups (P = 0.43).

CONCLUSION: HER2 dual-equivocal tumours share more similarity with HER2-negative disease in terms of clinico-pathologic features, HER2 mRNA levels, adjuvant systemic treatment patterns and disease outcome, which deserves further clinical evaluation.