Objective: To investigate the histopathological and immunohistochemical characteristics of benign apocrine cystic papillary hyperplasia of the breast with loss of myoepithelial cell layer. Methods: The clinical data, histopathological features and immunohistochemical profile of patients with benign apocrine cystic papillary hyperplasia of breast with loss of myoepithelial cell layer from January 2016 to December 2021 were examined, in which six patients were identified. Results: All six patients were female, aged 36-61 years (median 46 years), who presented with a breast mass; three cases were from the left breast and three cases were from the right breast. Microscopic examination of all cases showed breast hyperplasia with apocrine cysts, accompanied by different degrees of micropapillary and papillary hyperplasia of apocrine cells. One case was associated with lobular carcinoma in situ, and one case was associated with apocrine ductal carcinoma in situ with intraductal dissemination in adenosis. Immunohistochemical staining of CK5/6, p63, SMA, SMMHC, Calponin and CD10 showed complete absence of myoepithelial cell layer surrounding ducts in apocrine cystic papillary hyperplasia. Conclusions: The myoepithelial cells of apocrine cystic papillary hyperplasia of the breast may undergo abnormal changes and may even be completely lost. The diagnosis should be comprehensively considered along with cytomorphological and histological features to avoid overdiagnosis.
目的： 探讨乳腺良性大汗腺囊性乳头状增生性病变肌上皮缺失的病理形态学改变和免疫组织化学表型特征。 方法： 收集2016年1月至2021年12月解放军总医院第七医学中心病理科诊断的5例病例（2例本院，3例会诊）、首都医科大学大兴教学医院病理科诊断的1例病例，分析6例肌上皮缺失的乳腺良性大汗腺囊性乳头状增生性病变的临床资料、病理形态学特点及免疫组织化学染色表型，并复习相关文献。 结果： 6例患者均为女性，年龄36~61岁（中位年龄46岁）。左、右侧乳腺各3例，均有乳腺肿物。镜下观察，6例在乳腺增生病的背景病变内均可见良性大汗腺囊肿，同时伴有不同程度的大汗腺细胞的微乳头、乳头状增生；其中1例伴有经典型小叶原位癌，另有1例伴有大汗腺型导管原位癌及腺病腺管内播散。细胞角蛋白5/6、p63、平滑肌肌动蛋白、人肌球蛋白重链（SMMHC）、Calponin、CD10等免疫组织化学染色结果显示呈良性形态的大汗腺囊性乳头状增生性病变腺管周围的肌上皮细胞完全缺失。 结论： 乳腺良性大汗腺囊性乳头状增生性病变的肌上皮细胞可发生异常性改变，部分甚至完全缺失。诊断时应充分结合细胞形态学（异型性）及组织结构的改变综合考虑，以免过度诊断。.