Metaplastic breast carcinoma (MpBC) is a rare special histologic subtype of breast carcinoma characterized by the presence of squamous and/or mesenchymal differentiation. Most MpBCs are of triple-negative phenotype and neoadjuvant chemotherapy (NAC) is frequently utilized in patients with MpBC. The aim of this study was to evaluate response to NAC in a retrospective cohort of MpBCs. We identified 44 patients with MpBC treated with NAC at our center between 2002 and 2018. Median age was 48 years, 86% were clinical stage II–III, and 36% were clinically node-positive. Most (80%) MpBCs were triple-negative or low (1–10%) hormonal receptor positive and HER2 negative on pre-NAC biopsy. While on NAC, 49% showed no clinical response or clinico-radiological progression. Matrix-producing subtype was associated with clinico-radiological response (p = 0.0036). Post NAC, two patients initially ineligible for breast-conserving surgery (BCS) were downstaged to be eligible for BCS, whereas three patients potentially eligible for BCS before treatment became ineligible due to disease progression. Only one (2%) patient had a pathologic complete response (pCR). Among the 16 patients presenting with biopsy-proven clinical node-positive disease, 3 (19%) had nodal pCR. Axillary lymph node dissection was avoided in 3 (19%) patients who had successful axillary downstaging. Residual cancer burden (RCB) was assessed in 22 patients and was significantly associated with disease-free survival and overall survival. We observed a poor response or even disease progression on NAC among patients with MpBC, suggesting that NAC should be reserved for patients with inoperable MpBC.

化生性乳腺癌 (MpBC) 是一种罕见的特殊组织学亚型乳腺癌，其特征是存在鳞状和/或间充质分化。大多数 MpBC 具有三阴性表型，新辅助化疗 (NAC) 常用于 MpBC 患者。本研究的目的是在 MpBC 的回顾性队列中评估对 NAC 的反应。我们确定了 2002 年至 2018 年间在我们中心接受 NAC 治疗的 44 名 MpBC 患者。中位年龄为 48 岁，86% 为临床 II-III 期，36% 为临床淋巴结阳性。大多数 (80%) MpBC 在 NAC 前活检中呈三阴性或低 (1–10%) 激素受体阳性和 HER2 阴性。在使用 NAC 时，49% 没有表现出临床反应或临床放射学进展。基质产生亚型与临床放射学反应相关（p  = 0.0036）。NAC 后，最初不适合进行保乳手术 (BCS) 的两名患者降级为适合 BCS，而三名可能适合 BCS 的患者在治疗前由于疾病进展变得不适合。只有一名 (2%) 患者出现病理完全缓解 (pCR)。在出现活检证实的临床淋巴结阳性疾病的 16 名患者中，3 名 (19%) 有淋巴结 pCR。3 名（19%）成功腋窝降期的患者避免了腋窝淋巴结清扫。在 22 名患者中评估了残留癌症负担 (RCB)，并且与无病生存期和总生存期显着相关。我们观察到 MpBC 患者对 NAC 的反应不佳甚至疾病进展，这表明 NAC 应保留给不能手术的 MpBC 患者。