Rosen's Breast Pathology, 4e

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Chapter 11

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FIG. 11.10.  DCIS. A: The smaller duct contains solid carcinoma with low nuclear grade and the larger duct contains cribriform carcinoma with necrosis and high nuclear grade. B: The duct on left contains solid DCIS with intermediate-grade nuclei, and the duct on the right shows cribriform DCIS with relatively higher grade nuclei and calcification.

structural patterns are considered subsequent to a discus- sion of the current conventional structural classification.

nuclear grade micropapillary DCIS are usually relatively free of cellular debris or inflammatory cells. Calcifications that are granular, crystalline, or laminated occur particularly when carcinoma arises in a background of columnar cell hy- perplasia (CCH) (Fig. 11.11). In micropapillary DCIS, the normal epithelial layer of the duct is replaced by a single population of neoplastic cells. In any given case, the appearance of the carcinoma cells is relatively homogeneous, but cytologic heterogeneity can occur between individual cases. Most often, micropapillary DCIS is composed of cytologically low-grade homogeneous cells with a high nuclear-to-cytoplasmic ratio and dense, hyperchromatic nuclei (Figs. 11.12, 11.14, and 11.15). The nuclei typically vary little in size, and chromatin density is consistent between cells at the base and tip of micropapil- lae. Nuclei may be slightly smaller and darker at the surface, but marked disparity in these characteristics is a feature of micropapillary hyperplasia (see Chapter 9). At the margin of the duct, between papillary and arcuate structures, the neoplastic cells are typically arranged in a layer that rarely exceeds three cells in depth. The nuclei of the cells in the epithelium between micropapillae are usually unevenly dis- tributed in relation to the basement membrane (Figs. 11.12, 11.14, and 11.16). Persistent nonneoplastic epithelium be- tween micropapillae is a feature of micropapillary hyper- plasia rather than of micropapillary carcinoma. Mitoses are rarely present in low-grade micropapillary DCIS. The carci- noma cells tend to be so crowded and overlapping that their individual borders and cytoplasm cannot be identified. Oc- casionally, the cells have slightly more abundant cytoplasm, with apocrine-type protrusions at the luminal border. In one variant of this cell type, the nuclei of the tumor cells are contained in cytoplasmic blebs that are extruded into the duct lumen. Low-grade micropapillary DCIS can be found near some tubular carcinomas. These patients often have multifocal CCH with atypia and may also have LCIS

Structural Classification of DCIS Micropapillary DCIS consists of ducts lined by a layer of neoplastic cells giving rise at intervals to papillary fronds or arcuate formations protruding into the duct lumen. When micropapillae are inconspicuous or absent, this type of DCIS has been described as flat or “clinging” because the neoplastic epithelium seems to hug the basement membrane (Fig. 11.11). 116 The papillae are variable in appearance, rang- ing from short bumps or mounds to long slender processes (Fig. 11.12). The papillae lack a fibrovascular core and are composed of cytologically homogeneous carcinoma cells. Lesions in which the carcinomatous epithelium is supported by fibrovascular stroma should be classified as papillary carcinomas, even if the growth pattern is predominantly micropapillary (Fig. 11.13). Arcuate structures, commonly referred to as Roman bridge (or aqueduct) arches, occur when microlumens are formed under adjacent coalescent fronds or within a mound of neoplastic cells. These fenes- trations resemble the lumens formed in cribriform DCIS (Fig. 11.14). In conjunction with micropapillae, these arches are a feature of micropapillary DCIS and do not warrant a diagnosis of cribriform DCIS. In some situations, the micro- papillary and cribriform patterns merge (Fig. 11.15). Some samples of micropapillary DCIS develop complex, frond- forming structures without evolving into cribriform growth (Fig. 11.16). The appearance of the micropapillary fronds varies somewhat with the plane of individual histologic sections. Whereas some micropapillae are cut perpendicular to their long axis, others are seen sectioned tangentially or trans- versely, resulting in irregular nests of seemingly detached cell clusters in the duct lumen (Fig. 11.16). Ducts with low