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 247 consecutive 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 marker 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.