Prognostic significance of serum HER2 and CA 15-3 at the time of diagnosis of metastatic breast cancer.

BACKGROUND Serum HER2 testing allows the determination of real-time HER2 status during clinical course. The aim of this investigation was: (1) to study the prognostic significance of serum HER2 at the time of first diagnosis of metastatic breast cancer and (2) to evaluate its relationship to CA15-3 which is a surrogate marker for tumor load. MATERIALS AND METHODS Serum samples of 120 breast cancer patients were assayed for HER2 and CA15-3 at the onset of metastatic disease. RESULTS Forty-seven out of 120 (39%) metastatic breast cancer patients had elevated serum HER2 levels. The positivity rate of CA15-3 was 51%. The median survival after relapse (SAR) for HER2-positive patients was shorter (10 months, 95%-CI: 6-14 months) compared to the SAR of HER2-negative patients (19 months, 95%-CI:15-23 months) (p<0.01). The median survival of patients with increased CA15-3 was 13 months (95%-CI: 9-17 months) compared to 18 months (95%-CI: 15-21 months) for patients with normal CA15-3 concentrations (p<0.05). In the multivariate analysis serum HER2 was an independent prognostic marker for SAR even when adjusted for tumor load measured by CA15-3 levels. CONCLUSION Serum HER2 is a strong independent prognostic factor for survival after relapse in metastatic breast cancer even when adjusted for tumor load. Therefore, the prognostic significance of serum HER2 may not only be related to the tumor load but also to the biological behavior of the tumor.