Pleomorphic lobular carcinoma of the breast: an aggressive tumor showing apocrine differentiation.

Pleomorphic lobular carcinoma of the breast is a recently recognized subtype of invasive lobular carcinoma (ILC). Cytologic features are pleomorphic to a degree that contrasts with the cytologic uniformity of classic ILC. It is this feature that simultaneously gives its name to the tumor and highlights the difficulty of identifying it correctly and distinguishing it from ductal carcinoma. In our series of 10 cases, six tumors also contained lobular carcinoma in situ. Nodal metastases were typically sinusoidal. All tumors showed the dissociated, linear, and single file pattern of classic ILC, together with a targetoid distribution. Intracytoplasmic lumina were present in 50% of the tumors. An eosinophilic, slightly granular cytoplasm suggests the possibility of apocrine differentiation, a suggestion derived also from the frequent presence of foamy cells, a cell type previously identified in histiocytoid lobular carcinoma and shown to have apocrine features. The GCDFP-15 apocrine marker was positive in all 10 tumors, while all control ILCs were negative, confirming the presence of apocrine differentiation in pleomorphic lobular carcinoma. Six of 10 patients died within 42 months of diagnosis. Three other patients developed recurrence or distant metastases at short intervals. Pleomorphic lobular carcinoma is a very aggressive tumor. This behavior is perhaps predictable on the basis of tumor size at presentation and the frequency of nodal metastases. Since grading of lobular carcinoma is difficult, recognition of the pleomorphic subtype is useful in identifying a lethal variant.