PURPOSE This study aimed to elucidate the clinical implication of human epidermal growth factor receptor 2/centromeric probe for chromosome 17 (HER2/CEP17) ratio and HER2 immunohistochemistry (IHC) results in patients with HER2 fluorescence in situ hybridization (FISH)-positive metastatic breast cancer (MBC) who received first-line trastuzumab plus taxane chemotherapy.

METHODS Using clinical data of patients with HER2 FISH-positive MBC who received first-line trastuzumab plus taxane chemotherapy, we analyzed the clinical outcome according to the HER2/CEP17 ratio and HER2 IHC analysis.

RESULTS Fifty-two women were analyzed. The median age was 50 years (range 27-69 years). Patients with a HER2/CEP17 ratio ≥3.0 had significantly longer progression-free survival (PFS) (17.2 vs. 7.4 months; p = 0.002) with a tendency toward higher response rate (RR) (p = 0.325) and longer overall survival (OS) (p = 0.129). Patients with HER2 IHC 1+ had significantly shorter OS (14.0 vs. 42.4 months; p = 0.013) along with a tendency toward lower RR (p = 0.068) and shorter PFS (p = 0.220). In the multivariate analysis, HER2/CEP17 ratio <3.0 (p = 0.004) and Eastern Cooperative Oncology Group (ECOG) PS 2 (p = 0.015) were significant factors for shorter PFS, and HER2 IHC 1+ (p = 0.015) and ECOG PS 2 (p = 0.036) were significant factors for poor OS.

CONCLUSIONS Our data support that HER2/CEP17 ratios and HER2 IHC scores may predict clinical outcome after first-line trastuzumab plus taxane chemotherapy in patients with HER2 FISH-positive MBC.