Rosen's Breast Pathology, 4e

341

Ductal Carcinoma In Situ

FIG. 11.6.  (Continued)

to vacuolated or clear. There is variable nuclear pleomor- phism, sometimes manifested by prominent nucleoli. A more complete discussion of apocrine carcinoma can be found in Chapter 19. Clear cell DCIS is a poorly defined variant typically en- countered with solid and comedo patterns (Fig. 11.7). Some clear cell DCIS are composed of cells with an arrangement described as “mosaic” because of the appearance created by sharply defined cell borders (Fig. 11.7). A subset of lesions classified under this heading includes forms of apocrine car- cinoma. The presence of a monomorphic clear cell popu- lation is highly suggestive of DCIS. Occasionally, clear cell DCIS are strongly mucicarmine positive. Other clear cell le- sions are probably the in situ form of lipid-rich or glycogen- rich carcinomas discussed in separate chapters. Spindle cell DCIS may express neuroendocrine markers such as chromogranin, synaptophysin, and neuron-specific enolase. 111,112 The swirling growth pattern of cells in spindle cell DCIS mimics “streaming,” which is characteristically found in usual duct hyperplasia. Spindle cell DCIS often co- exists with cribriform DCIS. Small cell DCIS is extremely uncommon. The growth pat- terns are typically cribriform and solid or a mixture of these forms. When present by itself, the solid pattern of small cell DCIS can be distinguished from LCIS with the E-cadherin immunostain that demonstrates membrane reactivity in DCIS. E-cadherin staining is absent or fragmented and weak

in LCIS. “Neuroendocrine” DCIS is a less aggressive vari- ant of small cell carcinoma (SCC) that is typically charac- terized by solid growth and spindle cell with fine granular cytoplasm, immunoreactivity for neuroendocrine markers, and a lower proliferation rate than SCC. 112 The cellular composition of DCIS is typically mono- morphic . This term has been applied especially to cribri- form, solid, and micropapillary carcinomas. In this context, monomorphic means that there is overall homogeneity in the cytologic appearance of the DCIS cells—although there may be minor variation among cells in terms of amount of cytoplasm, nuclear size, etc. Variability in these parameters derives in part from differences in the plane in which they are sectioned. Cell and nuclear shape may be altered by the presence or absence of crowding in one or another part of the duct. The presence of a myoepithelial cell layer is not a consideration in judging whether a ductal proliferation is monomorphic. Dimorphic variants of DCIS consisting of two distinctly different populations of cells are unusual. The majority of dimorphic DCIS are papillary carcinomas (see Chapter 14). A dimorphic papillary DCIS with a small invasive compo- nent of mucinous carcinoma is illustrated in Figure 11.8. DCIS exhibits considerable tumoral heterogeneity, and in a given patient can have more than a single mi- croscopic structural, cytologic, or immunocytochemical phenotype. 76,113,114 Mixed histologic patterns are found in