Rosen's Breast Pathology, 4e

361

Ductal Carcinoma In Situ

FIG. 11.37.  DCIS, small cell. A: Focal squamous differen- tiation and central necrosis are shown. B: Small cell DCIS with lobular extension. C: The carcinoma in (B) is strongly E-cadherin immunoreactive, indicating ductal type.

of uniform cells, with cytologically well-differentiated to moderately differentiated nuclei (Fig. 11.47). The difficulty presented by these lesions is whether they should be classi- fied as entirely DCIS with “lobular cancerization” or as LCIS with duct extension. The E-cadherin stain will display strong membrane reactivity if the lesion is DCIS. E-cadherin stain- ing will be reduced and fragmented or absent in LCIS. The presence of a cribriform pattern suggests DCIS with lobular extension. Cells with apocrine differentiation are more consistent with ductal carcinoma. Ultimately, some difficult cases defy classification, even after careful consider- ation of all features and a diagnosis of combined intraductal and in situ lobular carcinoma may be made, accompanied by a description of the diagnostic issues presented in the par- ticular instance (Fig. 11.48). Coexistent intraductal and in situ lobular carcinoma in a single duct-lobular unit constitutes one of the most un- usual microscopic patterns of noninvasive breast carci- noma. 145 This diagnosis depends upon finding carcinoma with two distinctly different cytologic and structural pat- terns in a single duct. In these combined lesions, LCIS with the conventional small cell cytology is typically present within lobular glands as well as in a pagetoid distribution in the duct epithelium (Figs. 11.49 and 11.50). The duct lu- men contains a papillary, solid, or cribriform proliferation composed of more pleomorphic cells typically found in

that are separate from ducts with the classical features of comedo, papillary, or cribriform DCIS (Fig. 11.46). In some instances, the distinction is less clear, especially when the proliferation in the ducts and lobules is composed

FIG. 11.38.  DCIS in sclerosing adenosis. Cribriform carci- noma is present on the right. SA is present throughout the photograph.