Fig. 2.

Pleomorphic lobular carcinoma in situ (LCIS). A. Pleomorphic LCIS is characterized by a solid proliferation of dyscohesive cells, similar to classic LCIS, but with marked nuclear pleomorphism equivalent to high-grade DCIS. B. In this pleomorphic LCIS, many neoplastic cells have signet-ring cell morphology with large intracytoplasmic mucin-filled vacuoles that displace the nuclei to the periphery. Also noted are multinucleated cells, which may be present in pleomorphic LCIS but are not observed in classic LCIS. C and D. A subset of pleomorphic LCIS have apocrine features and are characterized by large cells with abundant eosinophilic, granular cytoplasm and large rounded nuclei with prominent nucleoli. E. Many neoplastic cells in this example of pleomorphic LCIS demonstrate prominent intracytoplasmic vacuoles, some of which contain a large eosinophilic globule. The finding of prominent intracytoplasmic vacuoles in an in situ lesion favors LCIS over DCIS, but may also create the false impression of glandular structures mimicking DCIS. Note the presence of associated invasive lobular carcinoma in the background. F. Pleomorphic LCIS is often, but not always, associated with comedo necrosis and calcifications.