Herein, we describe the first cases of neuroendocrine (NE) phenotype mammary carcinomas in which the NE nature of the tumors was confirmed only by insulinoma-associated protein 1 (INSM1), without expressions of traditional “gold standard” NE indicators. This is also the first analysis to use INSM1, a promising antibody with high sensitivity and specificity, in the field of breast oncology. Three patients were, respectively, 42-, 58-, and 64-year-old Japanese women with breast tumors showing characteristic NE morphologies. Immunohistochemically, these malignancies revealed diffuse nuclear expressions of INSM1, whereas chromogranin A and synaptophysin did not show distinct NE features in their cytoplasm. Based on the identification of INSM1 as well as our present immunohistochemical results, the frequency of detecting NE differentiation in systemic neoplasms, including breast NE phenotype cancers, is anticipated to increase such that, ultimately, our observations might contribute to the development of novel treatments including molecular targeted drugs for these tumor entities.

在此，我们描述了首例神经内分泌 (NE) 表型乳腺癌，其中肿瘤的 NE 性质仅通过胰岛素瘤相关蛋白 1 (INSM1) 证实，而没有表达传统的“金标准”NE 指标。这也是首次在乳腺肿瘤学领域使用INSM1进行分析，INSM1是一种具有高灵敏度和特异性的有前途的抗体。三名患者分别是 42 岁、58 岁和 64 岁的日本女性，她们的乳腺肿瘤显示出特征性的 NE 形态。免疫组织化学上，这些恶性肿瘤显示 INSM1 的弥漫性核表达，而嗜铬粒蛋白 A 和突触素在其细胞质中没有显示出明显的 NE 特征。基于INSM1的鉴定以及我们目前的免疫组化结果，