Herein, we report a case of synchronous bilateral triple negative invasive ductal breast carcinoma in a patient with discrepant pathologic response to neoadjuvant chemotherapy. Right and left breast cancer stages at the initial diagnosis were T1cN0M0 and T4dN3aM0, respectively. The patient was identified as a BRCA1 mutation carrier and treated with four cycles of adriamycin and cyclophosphamide, followed by four cycles of docetaxel. Bilateral breast cancer stages decreased with the first regimen. However, the bilateral breast cancers showed discrepant responses to chemotherapy with docetaxel. The right breast cancer showed a continuous tumor volume reduction while the left breast cancer showed marked progression. Finally, the tumor size was 0.3 cm and 12 cm in the right and left mastectomy specimens, respectively. As bilateral breast cancers of the same subtype may show discrepant responses to neoadjuvant chemotherapy, close monitoring and follow-up imaging are required to avoid delayed surgery.
