title: Serum HER2 levels determined by two methods in patients with metastatic breast cancer.
abstract: BACKGROUND
  The role and the optimal measurement method of serum HER2 levels are not defined in patients with metastatic breast cancer (MBC). We prospectively assessed the prognostic value of serum HER2 levels in MBC using two methods, enzyme immunoassay (EIA) and chemiluminescence immunoassay (CLIA).
  
  
  METHODS
  We collected blood samples from patients with MBC at baseline and at subsequent 3- to 4-week intervals up to 12 weeks. Samples were divided, and serum HER2 levels were determined using EIA and CLIA. We also determined whether serum HER2 levels had decreased by ≥20% at first follow-up. These results were evaluated against overall survival, progression-free survival, and tumor response.
  
  
  RESULTS
  We obtained 196 samples from 52 patients. In 59 samples from patients who received trastuzumab, serum HER2 positivity rates were significantly lower for EIA (n = 22) than for CLIA (n = 33, P = 0.042); in 137 samples from patients who did not receive trastuzumab, there was no significant difference in rates of serum HER2 positivity for CLIA (n = 83) and EIA (n = 80). Serum HER2 level at baseline, the level at first follow-up, and a decrease of ≥20% between baseline and first follow-up were not associated with overall survival, progression-free survival, and tumor response.
  
  
  CONCLUSIONS
  Chemiluminescence immunoassay was a more sensitive method than EIA for measuring serum HER2 levels in patients who received trastuzumab. However, because serum HER2 levels did not correlate with patient outcome, we do not currently recommend measuring serum HER2 levels by either method for prognostic evaluation in patients with MBC.
authors: Department of Breast Medical Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA.
authors: Naoki
authors: N
authors: Hayashi
authors: Seigo
authors: S
authors: Nakamura
authors: Yasuharu
authors: Y
authors: Tokuda
authors: Hiroshi
authors: H
authors: Yagata
authors: Atsushi
authors: A
authors: Yoshida
authors: Hidekazu
authors: H
authors: Ota
authors: Gabriel N
authors: GN
authors: Hortobagyi
authors: Massimo
authors: M
authors: Cristofanilli
authors: Naoto T
authors: NT
authors: Ueno
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