TTF1 and neuroendocrine neoplasm: The mammary origin of neuroendocrine tumors can be advocated when a ductal component is found in situ and/or immunohistochemical stains demonstrate positivity for CK7 while the negative stains each for TTF-1, CDX2, PAX8/PAX6 exclude the lung, gastrointestinal, and gastropancreatic/gastroduodenal tract origin, respectively [7,20].