Immunohistochemical determination of HER2 expression in breast cancer fromcore biopsy specimens: a reliable predictor of HEr2 status of the whole tumor

HER2 overexpression in breast cancer is associated with a poor prognosis, r esistance to endocrine therapy and chemosensitivity to anthracyclines and p aclitaxel. Moreover, trastuzumab (Herceptin(R)) shows therapeutic benefit i n patients with HER2 overexpressing tumors. Therefore, knowledge of the pre therapeutical HER2 status allows an optimal selection of patients for treat ment. In addition to a definitive histological diagnosis, core biopsies of tumors offer the opportunity to evaluate the HER2 status preoperatively. In 64 patients with invasive breast cancer, sections of core biopsies and of the subsequently removed whole tumor were investigated immuno-histochemical ly with the DAKO HercepTest(TM). Fifteen tumors (23%) revealed HER2 overexp ression, and 44 tumors (69%) were negative in both, the core biopsy and the whole tumor sections. Two core biopsies were negative whereas the correspo nding final specimen was 2+ positive. In 3 cases weak overexpression was ob served in the core biopsy, but the whole tumor was negative. The overall co ncordance of the results achieved at core biopsy and whole tumor sections w as 92% kappa = 0.8). A negative HER2 result on core biopsy was never associ ated with a score 3+ tumor specimen nor was there a case of negative whole tumor specimen with a preceding 3+ score in the biopsy. If one demands the highest degree of overexpression (3+), 100% of our study patients would hav e been selected correctly using the results on core biopsy alone. We thus c onclude, that the immunohistochemical investigation of core biopsies offers the opportunity for a valid preoperative estimation of HER2 overexpression .