NEUROENDOCRINE BREAST TUMOUR: A CHALLENGING ENTITY TUMOR NEUROENDOCRINO DE MAMA: UNA ENTIDAD DESAFIANTE Neuroendocrine breast carcinoma is a rare type of breast cancer with neuroendocrine differentiation which is found in around 2-5% of all invasive breast carcinomas. In most cases it is a challenge to get to the right diagnosis due to the sporadic number of cases and the need for special immunochemistry techniques, which are not routinely used. Due to the rare number of cases, it is difficult to update guidelines so that the correct diagnosis and treatment is decided. Our purpose is to present a clinical case in order to emphasize the importance of having this diagnosis in mind when breast cancer is found.