Introduction/Background Neuroendocrine neoplasms (NE) are uncommon heterogeneous tumors that arise from neuroendocrine cells all over the body. Breast primary NE tumors are sporadic and extremely rare entities, accounting for 0.1% of all breast cancers and less than 1% of all neuroendocrine tumors.

Methodology We report a series of five patients treated, at Salah Azaiz Institute of oncology, for primary neuroendocrine carcinoma of the breast from 2014 to 2021.

Results We present five cases with an average age of 59. 8 years. They presented with a single breast mass in four cases and multiple breast mass in one case. Physical examination revealed mobile, non-tender firm lesions. The average size of the tumor was 30 mm. In four cases, the mammography and ultrasonography revealed suspicious lesions classified as BIRADS 5. The tumor was classified as BIRADS 4c in one case. Chest, abdomen and pelvis scan revealed no evidence of distant metastases in all cases. Microbiopsy was performed prior to surgery in three cases. Breast conserving surgery was performed in three cases and modified radical mastectomy in the two others. In all cases, the final pathology study concluded to a neuroendocrine carcinoma with no metastatic lymph nodes. On immunohistochemical evaluation, the tumor cells stained strongly positive for estrogen and progesterone receptors (in two cases) and were positive for synaptophysin (all cases), also for chromogranin (in three cases). Two patients received adjuvant radiotherapy; one patient had chemotherapy only, while chemotherapy and radiotherapy associated to hormonotherapy were given to the two others. The mean time of follow-up was 21. 8 months, and there were no recurrence or distant metastases noticed.

Conclusion Due to their rarity and heterogeneity, primary breast neuroendocrine tumors are underappreciated. They have a poor prognosis. There are no specific treatment guidelines, and the available data is primarily based on case reports.