Extracellular domain of HER2: A useful marker for the initial workup and follow-up of HER2-positive breast cancer

Purpose: The extracellular domain (ECD) of the HER2 receptor is proposed as a real-time marker of HER2-positive breast cancer (BC). In this study, ECD-HER2 levels were compared with standard clinical and pathological prognostic factors. Patients and methods: In 247consecutive patients (116 with early or localized BC, 116 with advanced or metastatic BC, and 16 with benign mastopathies), serum ECD-HER2 levels were measured. In 116 advanced-disease patients ECD-HER2 status was also studied by immunohistochemistry (IHC) and compared with established clinical and pathological variables. Results: Mean serum ECD-HER2 value was 19.62 ng/ml (median 10.35, range 3 - > 250). Mean value in benign mastopathies was 9.04 ng/ml, 9.4 ng/ml in early disease and 34.5 ng/ml in advanced disease. No difference between benign mastopathies and early BC was observed, while significant difference between early and advanced BC (p < 0.001) was noted. However in advanced-disease patients a positive correlation of ECD-HER2 with IHC (p= 0.002), disease grade (p= 0.034) and level II axillary node involvement (p= 0.011) was noted, as well as a significant negative correlation with estrogen receptor (ER) and progesterone receptor (PR) (p = 0.035 and p= 0.011, respectively). Conclusion: ECD-HER2 is a reliable market-for breast cancer as suggested from the existing literature; therefore, its integration in the initial workup and follow-up routine of breast cancer particularly the HER2-positive, is proposed.