The ultrastructure of medullary, atypical medullary and non‐medullary carcinomas of the breast

Three medullary, eight atypical medullary and four non-medullary carcinomas of the breast were studied by transmission electron microscopy. Detailed comparison of a number of structural, cytoplasmic and nuclear features failed to confirm previous suggestions that medullary carcinoma cells have a distinctive ultrastructure. Electron microscopy is thus unlikely to be useful in the differential diagnosis of the tumours, nor does it suggest a basis for the good prognosis of medullary carcinoma.