Rosen's Breast Pathology, 4e

349

Ductal Carcinoma In Situ

FIG. 11.17.  DCIS with squamous metaplasia. A: Isolated foci of squamous metaplasia are present in the micropapillary carcinomatous epithelium ( arrow ). B: Squamous metaplasia in solid DCIS.

adenoid cystic carcinoma (AdCC) or a complex papilloma. Collagenous spherulosis that is usually associated with hy- perplastic duct lesions can, in rare instances, be involved by DCIS (Fig. 11.20). The resultant structure resembles cribri- formDCIS because the spherules simulatemicrolumens. The presence of collagenous spherulosis can be confirmed with either heavy-chain myosin or SMA immunostain, which will highlight myoepithelial cells at the perimeter of spherules or immunostains for basement membrane components (such as laminin or collagen IV). LCIS can also inhabit collagenous spherulosis. The distinction between intraductal and in situ lobular carcinoma in collagenous spherulosis depends on cytologic features of the lesion and can be confirmed with the E-cadherin or p120 immunostains. The appearance of any adjacent coexisting in situ carcinoma not in collagenous spherulosis can also be helpful. The secondary microlumina in cribriform DCIS tend to be round or oval, with smooth luminal edges bordered by cu- boidal cells (Fig. 11.21). The distribution of microlumina is variable. In some instances, the spaces are spread across the entire duct or concentrated toward the center. The presence

of microlumina entirely at the periphery of the duct is usu- ally an indication of hyperplasia, but this appearance may be mimicked in cribriform DCIS when the center of the duct is destroyed by necrosis (Fig. 11.22). It is a hallmark of cribriform DCIS that the microlumina be surrounded by a homogeneous cell population that is uniformly distributed throughout the duct. The microlumina may contain secre- tion, small numbers of degenerated or necrotic cells, and punctate calcifications. Bands of neoplastic cells between and around the mi- crolumina in cribriform DCIS are described as “rigid,” a term that refers to the uniform, nonoverlapping, distribu- tion of polygonal cells in contrast to the streaming pattern of overlapping, frequently oval cells in duct hyperplasia (Fig. 11.23). Polarization of the cells in an orderly fashion around the microlumina contributes to the “rigid” appear- ance. The most orderly type of cribriform DCIS is composed of cuboidal to low columnar monomorphic cells with low nuclear grade. Nucleoli are inconspicuous or absent, and mitoses are rarely encountered. The cells usually have sparse cytoplasm. An apocrine variant is composed of cells with low- to intermediate-grade nuclei and more abundant gran- ular eosinophilic cytoplasm (Fig. 11.24). Secretion is found in some but not all cribriform microlumina, and when pres- ent it can form small calcifications. Cribriform DCIS with necrosis, mitotic activity, and poorly differentiated nuclear grade is rare, and these lesions tend to have less well-defined microlumina (Fig. 11.25). The cribriform pattern of carci- noma may either represent DCIS or invasive carcinoma. The latter disease is an uncommon entity that is characterized by an infiltrative pattern of growth (Chapter 26). In some circumstances, it may be difficult to distinguish between cribriform and other structural subtypes of DCIS, and in these instances the choice is sometimes arbitrary. ­Fibrovascular stroma and myoepithelial cells are not present in the epithelium of cribriform DCIS, but myoepithelial cells may persist at the periphery of the involved duct (Fig. 11.4). Solid papillary DCIS in which fibrovascular stroma is clearly evident occasionally has a prominent fenestrated pattern that mimics cribriform DCIS. The stromal component of

FIG. 11.18.  DCIS, micropapillary clear cell type.