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Evaluation of CD56 and CD57 immunostainings for discrimination between endocrine ductal carcinoma in situ and intraductal papilloma

Endocrine ductal carcinoma in situ (E‐DCIS) is an intraductal carcinoma characterized by endocrine features and expression of neuroendocrine markers. E‐DCIS and intraductal papilloma (IDP) resemble in their clinical features. However, the former is an intraductal carcinoma, and the latter is an intraductal benign lesion. It is sometimes difficult to distinguish E‐DCIS from IDP because both can show near solid intraductal cellular proliferation. Discrimination between lesions is important not only histopathologically, but also clinically. This study aimed to evaluate the applicability of CD56 and CD57 for the discrimination between E‐DCIS and IDP. Specimens were obtained from 17 E‐DCIS patients as the subject group, and 27 IDP patients as the control group, diagnosed in St Marianna University Hospital. E‐DCIS was diagnosed using Chromogranin A, Synaptophysin, and Grimelius stainings by the premise of histopathological features. These specimens were subjected to CD56, CD57 immunostainings. Staining results were compared between E‐DCIS and IDP. In our study, CD56 revealed significant differences for distinguishing E‐DCIS from IDP as determined by Fisher's test (cutoff: not less than 33–67%< immunopositivity, P < 0.05). We found that not only E‐DCIS but also IDP revealed immunopositivity for CD56. However, it is considered that E‐DCIS diagnosis is possible by diffuse immunopositivity of CD56 after having been based on histopathology.