P1-12-18: Change in HER2 Status in HER2 Positive Operable Breast Cancer Patients Treated with Neoadjuvant Chemotherapy with or without Anti-HER2 Therapy: Analysis of Two Consecutive Cohorts.

Abstract

Abstract Introduction: emerging literature data have shown a change of HER2 expression from primary tumors to metastatic deposits. Tumor heterogeneity, genetic drift as well as selective pressure of adjuvant therapy have been suggested to explain this phenomenon. Aim of the present analysis is to evaluate the change in HER2 expression after neoadjuvant chemotherapy with or without anti-HER2 agents. Methods: two consecutive cohorts of HER2+ breast cancer patients treated with neoadjuvant therapy were identified from a prospectively maintained database including 310 patients. The first cohort (A) includes 38 patients enrolled before 2005, treated with chemotherapy alone. The second cohort (B) includes 48 patients treated with neoadjuvant chemotherapy in combination with antiHER2 agents (trastuzumab or lapatinib). HER2 expression was evaluated by IHC on pre-treatment core biopsy (tru-cut with 14 gauge needle) and on surgical specimen after neoadjuvant therapy. FISH analysis was performed on IHC 2+ samples. Results: The two cohorts were balanced in respect of tumor stage, patient age, and HR expression. In particular, a co-expression of HER2 and HR was observed in 60% of the patients in cohort A and in 70% of the patients in cohort B (p=0.2). Patients in cohort B have a significantly higher rate of pathologic complete response (pCR) in comparison to cohort A (45% vs 11%, p=0.001). A change in HER2 expression from biopsy to post-therapy samples was observed in 39% of the patients in cohort A vs 12% of the patients in cohort B (p=0.02). No patients with pCR have recurred so far vs 25% of the patients with less than pCR (p=0.005). The rate of recurrence was significantly higher for patients experiencing a change in HER2 expression (50% vs 19%, p=0.018). Conclusion: contrary to our expectations, patients not receiving anti-HER2 therapy as part of neoadjuvant therapy were more likely to have a change in HER2 status vs patients receiving anti-HER2 neoadjuvant therapy. The change in HER2 status has a negative prognostic impact. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P1-12-18.