Influence of neoadjuvant chemotherapy on HER2/neu status in invasive breast cancer.

Introduction: Reliably estimating HER2/neu expression in breast cancer is important for predicting patient prognosis and optimizing adjuvant therapeutic strategies. In this retrospective cohort study, effects of NAC on HER2/neu status in invasive breast cancer were evaluated, and the related factors were analyzed.

Patients And Methods: One hundred thirty-one patients with primary breast cancer were treated with anthracycline- and/or taxane-based NAC. HER2/neu status was evaluated by IHC on core needle biopsies of primary tumors before NAC and surgical resection specimens of post-NAC residual breast cancers or tumor-positive axillary lymph nodes. Thirty-two pairs of specimens with discordant HER2/neu IHC scores were analyzed by fluorescence in situ hybridization (FISH).

Results: A significant difference in HER2/neu status by IHC between core needle biopsies and surgical resection specimens in patients receiving NAC was observed. After NAC, 23.4% (29 of 124) of tumors showed downregulated HER2/neu expression by IHC. Alterations of HER2/neu IHC scores did not significantly correlate with tumor subtype, pathologic response to NAC, adjuvant regimen, or time interval from the last chemotherapy to surgery. HER2/neu protein overexpression level was associated with favorable pathologic response to anthracycline and taxane-based chemotherapy. However, tumors with altered HER2/neu IHC scores after NAC revealed stable HER2/neu gene amplification/nonamplification by FISH analysis.

Conclusion: Neoadjuvant chemotherapy for breast carcinoma resulted in the HER2/neu status alteration by IHC, but they have stable gene amplification status by FISH. HER2/neu protein overexpression indicated greater sensitivity to neoadjuvant anthracycline- and taxane-based chemotherapy. Thus, retesting HER2/neu IHC status in residual tumors after NAC should be considered in order to optimize adjuvant systemic therapy.