Medullary carcinoma of the breast: an ultrastructural morphometric study of nine cases.

Ultrastructural and morphometric features of 10 medullary carcinomas of the breast (MC) were investigated. Cases with a long follow-up were selected by applying stringent histologic criteria. All tumors had a homogeneous appearance by light microscopy. Under transmission electron microscopy, they showed occasional intracellular lumen formation or keratinization. In one tumor squamous differentiation was prominent and diffuse. Tumors with lymph node metastases possessed over 40% more desmosomes than nonmetastatic tumors. The number of cells with three or more nucleoli per nuclear section was significantly higher in metastatic than in nonmetastatic tumors (p = .02). Classic cases of MC of the breast display a relatively uniform appearance. However, subtle differences can be identified between metastatic and nonmetastatic tumors by ultrastructural morphometry. Although these differences are not associated with changes in the outcome of patients in this study, they seem to bear some relationship to the peculiar behavior of MC.