Fibroadenoma with "immature-like" type of usual ductal hyperplasia.

We herein report a case of the breast fibroadenoma with foci of so-called immature variant of the conventional ductal hyperplasia. This type of usual ductal hyperplasia is histologically characterised by encircling intraductal proliferation of large cells with pale to amphophilic cytoplasm and large nuclei which vary in shape and in staining quality of the chromatin. We showed here, using the cytokeratin immunohistochemistry, that the proliferating cells were not of immature but rather mature immunohistochemical phenotype. Because of the presented discordance between immature histology and mature immunohistological profile we suggest that this rare type of usual ductal hyperplasia should be called "immature-like".