人类表皮生长因子受体2（HER2/neu或ErbB2）阳性乳腺癌占所有乳腺癌的15%-20%。HER2阳性乳腺癌在乳腺X线摄影或超声检查中最常见的表现是不规则肿块，有棘状边缘，通常含有钙化；在磁共振成像中，HER2阳性乳腺癌可出现为肿块或非肿大增强。在组织病理学分析中，HER2阳性乳腺癌往往是中度到高核级别，具有局部复发和转移的风险增加以及整体预后较差。然而，靶向单克隆抗体治疗，如特拉吉珠单抗和帕珠单抗，提供更好的局部-区域控制，并导致生存预后改善。随着新辅助治疗的发展，包括单克隆抗体、紫杉醇和蒽环类，女性现在可能能够进行乳腺保留治疗和前哨淋巴结活组织检查，而不需要乳房切除和腋窝淋巴结清扫。因此，放射科医师在评估局部-区域疾病的范围和新辅助治疗的反应时，在影像学方面的作用对于手术规划和辅助治疗是很重要的。然而，治疗反应的评估仍然存在困难，不同的影像学检查可能会导致对疾病的低估或高估，与手术病理分析相比程度不同。特别是在乳腺X线摄影中，钙化的存在特别难以与化疗后的病理分析结果相关联。乳腺磁共振成像结果仍然是预测病理反应的最佳预测指标。作者通过多模式影像学回顾和病理相关性，评估HER2阳性肿瘤的初期表现、新辅助化疗的不同反应及在评估残余癌症负荷时的挑战。©RSNA，2023年本文的测验问题可通过在线学习中心获得。

Human epidermal growth factor receptor 2 (HER2/neu or ErbB2)-positive breast cancers comprise 15%-20% of all breast cancers. The most common manifestation of HER2-positive breast cancer at mammography or US is an irregular mass with spiculated margins that often contains calcifications; at MRI, HER2-positive breast cancer may appear as a mass or as nonmass enhancement. HER2-positive breast cancers are often of intermediate to high nuclear grade at histopathologic analysis, with increased risk of local recurrence and metastases and poorer overall prognosis. However, treatment with targeted monoclonal antibody therapies such as trastuzumab and pertuzumab provides better local-regional control and leads to improved survival outcome. With neoadjuvant treatments, including monoclonal antibodies, taxanes, and anthracyclines, women are now potentially able to undergo breast conservation therapy and sentinel lymph node biopsy versus mastectomy and axillary lymph node dissection. Thus, the radiologist's role in assessing the extent of local-regional disease and response to neoadjuvant treatment at imaging is important to inform surgical planning and adjuvant treatment. However, assessment of treatment response remains difficult, with the potential for different imaging modalities to result in underestimation or overestimation of disease to varying degrees when compared with surgical pathologic analysis. In particular, the presence of calcifications at mammography is especially difficult to correlate with the results of pathologic analysis after chemotherapy. Breast MRI findings remain the best predictor of pathologic response. The authors review the initial manifestations of HER2-positive tumors, the varied responses to neoadjuvant chemotherapy, and the challenges in assessing residual cancer burden through a multimodality imaging review with pathologic correlation. © RSNA, 2023 Quiz questions for this article are available through the Online Learning Center.