Metaplastic breast cancer (MBC) is a malignancy characterized by the histologic presence of two or more cellular types, commonly a mixture of epithelial and mesenchymal components. MBC is rare relative to invasive ductal carcinoma (IDC), representing less than 1% of all breast cancers. Other than a lower rate of lymph node metastases, MBC tumors display poorer prognostic features relative to IDC. Due to its low incidence and pathological variability, the ideal treatment paradigm for MBC is unknown. Because of its rarity, MBC has been treated as a variant of IDC. Despite similar treatment regimens, however, patients with MBC have worse outcomes. Recent research is focused on biological differences between MBC and IDC and potential novel targets for chemotherapeutic agents. This paper serves as a summation of current literature on approaches to the multidisciplinary treatment of patients with MBC. 1. Introduction Metaplastic breast cancer (MBC) is a rare malignancy characterized by the histologic presence of two or more cellular types, commonly a mixture of epithelial and mesenchymal components [1–6]. MBC represents 0.25–1% of breast cancers diagnosed annually [1, 7, 8]. Due to its relative rarity and heterogeneous histologic presentation, the pathologic diagnosis of MBC is difficult. The World Health Organization (WHO) recognized MBC as a unique pathologic entity in 2000. Since then, the incidence of MBC has risen, likely representing an increased recognition by pathologists [8, 9]. Overall, greater than 70% of patients with MBC present with American Joint Committee on Cancer (AJCC) stage II or greater disease as compared to approximately 50% of patients with IDC [8]. Compared to patients with IDC, those with MBC have worse outcomes with 5-year survival rates ranging from 49% to 68% [1, 10, 11]. The optimal treatment strategies for MBC are unknown. Management of MBC has largely paralleled that of IDC, despite growing evidence that MBC is a distinct entity that lies along the spectrum of basal-like breast cancers. This paper serves as a summation of current literature and approaches to the multimodality treatment of patients with MBC. 2. Surgical Therapy The surgical treatment of MBC has largely paralleled that of IDC. With the publication of NSABP B-06 trial results, the surgical approach to IDC shifted from mastectomy to breast conservation therapy for appropriate patients. Large tumors (≥5？cm) are a relative contraindication to breast conservation therapy [12] and even less extensive tumors may preclude breast conservation in smaller-breasted patients.
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