ABSTRACT
This study aims at reviewing 26 cases of medullary carcinoma by routine morphologic analysis according to the criteria described for each subtype. An electron-microscopic study is carried out on selected cases to clarify ultrastructural differences between the 3 subtypes. Among the 26 cases studied 12 were TMC. Ultrastructural analysis has shown many points of similarity between TMC and AMC and revealed signs of their ultrastructural differentiation in spite of their light microscopic undifferentiation. On the other hand, NMIDC is undifferentiated on ultrastructural level. These findings explain reports of a significantly better prognosis of TMC and AMC over NMIDC grade III. The previous proposal of a simplification to this subtying can be approved, putting into consideration that NMIDC should be defined separately as an infiltrating duct carcinoma with dense lymphocytic infiltrate E/M should be performed to cases in the borderline between AMC and NMIDC