Neuroendocrine breast tumours: breast cancer or neuroendocrine cancer presenting in the breast?

Neuroendocrine tumours (NET) of the breast are rare. Diagnosis depends on close scrutiny of core- or excisional-biopsy specimens for characteristic growth patterns (papillary, nesting or mixed), which should trigger immunohistochemical staining for neuroendocrine markers (in particular chromogranin and synaptophysin). The diagnosis is confirmed if a) >50% of the tissue specimen demonstrate neuroendocrine markers and b) in-situ ductal carcinoma is identified and/or imaging modalities exclude extra-mammary sites. Our literature search including the non-English literature identified 66 articles with data on 123 cases, including our own. Oestrogen receptors are not diagnostic for NET's of the breast as they are found in tumours of non-mammary origin, too. Half of reported cases of neuroendocrine tumours have axillary lymph node involvement. Breast-conserving surgery (wide local excision ± axillary clearance) is commonly performed for suitable tumours. Chemotherapy regimens utilised are commonly either platinum- (as for small-cell cancers) or anthracycline-based (as for primary breast cancers). Best management remains unknown.