The immunohistochemical features of 5 ductal adenomas of the breast we
re investigated. The tumours were composed by tubular glands lined by
cells with both luminal and basal/myoepithelial immunophenotypes. Tubu
les were encircled by an intact basement membrane as demonstrated by s
taining for laminin and type IV collagen. Areas of dense fibrosis, a u
sual finding in these lesions, stained for fibronectin, type III colla
gen and contained vimentin and actin positive spindle cells, consisten
t 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 p
apillomas.