Introduction/Background Primary neuroendocrine carcinoma of the breast is a rare histopathological variant. It represents 0.1% of breast cancers.

Methodology We report a case treated in the department of oncology-radiotherapy of Sousse with the aim of detecting the anatomoclinical,therapeutic and evolutionary aspects of this cancer.

Results We report the case of a 52-year-old patient. The history of her disease was marked by the appearance of a nodule of the left breast. An echo mammogram was performed and showed a 2.5 cm solid and irregular nodule in the inner quadrant of the left breast classified as ACR4. This nodule increased in size with the appearance of permeation nodules and bleeding with a new mammogram showing a large tumor in the left breast measuring 14 cm associated with carcinomatous mastitis and homolateral axillary adenopathies. The biopsy concluded to a poorly differentiated neuroendocrine carcinoma of the breast. Hormone receptors were positive, HER2 labelling was negative and Ki67 was evaluated at 80%. the tumor was classified as T4dN1M1a (costal involvement). The patient received 3 courses of FEC100 but due to clinical progression, a second line of VP16-cisplatin-based chemotherapy was indicated.The evolution was marked by an increase in tumor size with spontaneous bleeding.The patient underwent left locoregional radiotherapy at a dose of 50Gy (2Gy per fraction) with a 20Gy boost on the tumor including the costal lesion followed by a left mastectomy.The evolution was marked by adrenal and cerebral progression 8 months after surgery. Given the refractory nature of chemotherapy, only hormone therapy was persued.the patient underwent total brain irradiation radiotherapy at a dose of 20 Gy in 5 fractions with good tolerance.

Conclusion Primary neuroendocrine carcinoma of the breast is a rare entity with a poor prognosis. The literature has been limited to case reports in which the management has been similar to our case.