Pleomorphic lobular carcinoma is a recently described entity separated from classical lobular carcinoma by cytologic pleomorphism. It can have an aggressive clinical course with a higher frequency of recurrence. Histologic differentiation with ductal carcinoma may be difficult, but it is important for this differentiation to be made. E-cadherin is a transmembrane glycoprotein, and complete loss of E-cadherin expression has been observed in invasive lobular carcinoma and lobular carcinoma in situ. Ductal carcinoma retains at least some expression of E-cadherin. We examined the pattern of E-cadherin expression in a series of 14 cases of pleomorphic lobular carcinoma by immunohistochemistry. Twelve of the 14 cases showed no staining (86%); the remaining two cases exhibited 10% to 25% positive cells. In cases with histologic equivocal features, immunohistochemical detection of E-cadherin expression can be a useful diagnostic aid for the differentiation of pleomorphic lobular and ductal carcinoma.
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