Breast neuroendocrine carcinoma (NECB) is a rare type of breast tumor. Large-cell neuroendocrine carcinomas of the breast (LCNECB) are a special and rare histological subtype of NECB. Here, we present a case of a 59-year-old woman who was diagnosed with an LCNECB. A mass in the upper outer quadrant of the right breast was revealed via imaging. A histological examination showed the tumor cells were composed of clusters of large cells with obvious atypia that were polygonal or irregularly shaped. The patient underwent a right-breast-conserving radical surgery and sentinel lymph node biopsy (SLB). A histopathological examination revealed that the tumor of the right breast was 2.5 × 2 cm in size with vascular invasion, and the sentinel lymph node was negative. The immunohistochemical results showed that the tumor cells were diffuse and positive for chromogranin A (CgA), synaptophysin (Syn), and INSM1. The patient successfully completed chemotherapy and radiotherapy and is currently undergoing endocrine therapy.