Abstract
We report a case of synchronous locally advanced bilateral breast cancer with different pathological responses to neoadjuvant chemotherapy with different biological character. The patient had presented bilateral breast cancer: the left breast cancer was hormone receptor negative, human epidermal growth factor receptor-2 (HER2) positive, and classified as T4bN1M0, stage IIIb, while the right was hormone receptor positive, HER2-negative, and classified as T4bN0M0, stage IIIb. We administered four cycles of anthracycline-based therapy followed by 12 weekly cycles of taxane with trastuzumab for neoadjuvant chemotherapy. We had achieved a significant left tumor reduction after each chemotherapy, but not right tumor. Bilateral modified radical mastectomies with axillary lymph-node dissection were performed. The therapeutic effect in the left was determined as a pathological complete response, in contrast to the right side. She has no recurrence for more than five years, though she had advanced cancer with oncologic emergency. This case could be an informative experience to understand the relation of tumor biology and response to systemic therapy.