A neoplasm that arises from the breast and is composed of cells of neuroendocrine origin. Most cases are neuroendocrine carcinomas. Primary carcinoid tumors of the breast are very rare. The disease is breast neuroendocrine neoplasm (MONDO_0002485). Also known as: breast NET, breast endocrine neoplasm, breast neuroendocrine tumor, breast neuroendocrine tumor, well differentiated, low or intermediate grade, breast neuroendocrine tumour, neuroendocrine neoplasm of breast, neuroendocrine neoplasm of the breast, neuroendocrine tumor of the breast.