Background: Serum HER2 testing allows the determination of the real-time HER2 status of breast cancer patients. The aim of this investigation was to study (i) whether changes of serum HER2 status occur during the clinical course of breast cancer and (ii) to evaluate the prognostic significance of serum HER2 status, at the time of first diagnosis of primary breast cancer and at the onset of metastatic disease, for survival after relapse (SAR).
Materials and methods: HER2 serum levels were retrospectively measured in 152 breast cancer patients at the time of first diagnosis of breast cancer and at the onset of metastatic disease by enzyme immunoassay.
Results: Twenty-seven out of 152 (18%) patients had elevated HER2 serum levels at the time of first diagnosis of breast cancer. In contrast, 56 out of 152 (37%) patients showed elevated serum HER2 levels when metastases were diagnosed. A change of serum HER2 status during clinical course was observed in 43 out of 152 (28%) patients. Serum HER2 status at the time of first diagnosis of breast cancer had no impact on survival after relapse (SAR) (p = 0.4). However, the median SAR for serum HER2-positive patients at the onset of metastatic disease was significantly shorter (8 months, 95% CI: 3-12) compared to patients serum HER2-negative at this time (18 months, 95% CI: 14-22) (p < 0.01).
Conclusion: Serum HER2 status can change during the course of disease. Therefore, the serum HER2 status should be re-evaluated at the time of diagnosis of metastatic disease to optimize treatment decisions.