Ductal adenoma of the breast. An immunohistochemical study of five cases.

The immunohistochemical features of 5 ductal adenomas of the breast were investigated. The tumours were composed by tubular glands lined by cells with both luminal and basal/myoepithelial immunophenotypes. Tubules were encircled by an intact basement membrane as demonstrated by staining for laminin and type IV collagen. Areas of dense fibrosis, a usual finding in these lesions, stained for fibronectin, type III collagen and contained vimentin and actin positive spindle cells, consistent with myofibroblasts. These observations confirm a double epithelial and myoepithelial differentiation in these lesions and seem to support the suggestion that ductal adenomas result from sclerosis of ductal papillomas.