Adenocarcinoma with neuroendocrine differentiation is defined as typical acinar or ductal adenocarcinoma without a detectable neuroendocrine morphology (such as nuclear molding and peripheral palisading) and with neuroendocrine differentiation, demonstrated only by immunohistochemical detection of at least one of three neuroendocrine markers (CHGA [chromogranin A], SYP [synaptophysin], or NCAM1 [CD56, NCAM]). Here, SYP is linked to invasive ductal breast carcinoma.