E-cadherin reactivity of 95 noninvasive ductal and lobular lesions of the breast - Implications for the interpretation of problematic lesions

Studies suggest that E-cadherin is useful to classify epithelial breast les ions as ductal or lobular, but extensive experience with this antibody is l acking. We studied reactivity of lesions with classic and indeterminate mor phologic features. We reviewed 95 lesions and divided them into unanimous a nd non unanimous diagnosis groups; the unanimous group served as benchmark lesions to which E-cadherin reactivity could be standardized and compared. All 37 ductal lesions in the unanimous group had strong, diffuse E-cadherin reactivity. Two of 22 classic lobular carcinoma in situ (LCIS) lesions had sparse E-cadherin-reactive lobular cells within a few terminal duct lobula r units. Neither displayed transition from nonreactive to reactive cells. O f 36 lesions in the nonunanimous group, 19 had insufficient morphologic fea tures for definitive classification. Only 6 of 19 were E-cadherin reactive, including several minimally proliferative lesions. The other 17 lesions in the nonunanimous group had LCIS and ductal carcinoma in situ (DCIS) featur es. All had no E-cadherin, or strong membrane reactivity of constituent cel ls in varying proportions, without a transition between reactive and nonrea ctive cells. Results suggest that the majority of morphologically nondiagno stic atypical lesions are lobular, including those associated with DCIS. E- cadherin seems to be absent in most lobular lesions.