Ductal adenoma of the breast: a lesion which can mimic carcinoma.

Twenty-four cases of a solid benign tumour of breast ducts are described, for which we propose the name 'ductal adenoma'. The lesion consists of a single nodule or multiple nodules involving medium size and small ducts, but not major subareolar ducts. It presents as a palpable lump, and is not associated with a nipple discharge. Clinically, radiologically and macroscopically, it can simulate malignancy because of its occurrence in older age groups, frequent microcalcification and the firmness and irregularity of many lesions. Fibrous sclerosis sometimes results in distortion with apparent invasion of surrounding tissue. It can be mistaken for carcinoma both on frozen and paraffin sections. Differentiation into epithelial and myoepithelial cells is the most reliable criterion in the recognition of this lesion as benign. It has microscopic affinities with ductal papilloma, on the one hand, and with salivary-type adenoma, on the other. Ductal adenoma constitutes the third major type of adenoma in the breast, in addition to the already widely recognized nipple adenoma and tubular adenoma.