33 Special Types of Invasive Breast Carcinoma: Diagnostic Criteria ...

eceptor-positive (21).
Microscopically, tubular carcinomas have stellate irregular margins of haphazard
invasive glands separated by abundant desmoplastic stroma (22,23). The glands have
open lumina with irregular, sharply angulated contours, and are composed of a single
layer of neoplastic epithelial cells (2). Some minority of glands can have more
complex growth (42) Much less commonly, the glands are round or oval and of
relatively uniform caliber, However, when faced with a population of rounded glands,
microglandular adenosis should be a diagnostic consideration, especially if the lumens
contain eosinophilic or colloid-like secretion. The cells in tubular carcinoma are
homogeneous with cuboidal or columnar shapes and round or oval hyperchromatic
nuclei that tend to be basally oriented and about the size of the nuclei in the adjacent
benign breast epithelium (i.e., nuclear grade 1). Nucleoli are inconspicuous or
inapparent, and mitoses are rarely seen. Cytoplasmic snouting is commonly present at
the luminal cell border. The cytoplasm is usually amphophilic. EM shows an absent
or, more commonly, a discontinuous basal lamina. Although some suggest 75%, as
indicated above, I only diagnose tubular carcinoma when over 90% of the tumor
exhibits the classic tubular growth pattern. When more than 10% of the tumor
consists of InvDC, NST, I make the diagnosis of mixed ductal and tubular carcinoma.
Nonetheless, there are studies suggesting that 75% is an appropriate cut point, because
the prognosis is reported as favorable when tumors consist of at least 75% tubular
elements (3,5,11,18,22).
The invasive component of cribriform carcinoma has a sieve-like or irregular
cribriform growth pattern very similar to low-grade cribriform intraductal carcinomas.
The round and angular masses of uniform, well-differentiated tumor cells are
embedded in desmoplastic stroma. In some areas it may be difficult to distinguish
between the intraductal and invasive components of the lesion. Yet, the invasive
cribriform clusters are usually irregular in outline, which is in contrast to the rounded
even contours of intraductal carcinoma. When present, myoepithelial cells serve as a
clue to intraductal carcinoma. Mucin-positive secretion is present in varying amounts
within these lumens. As previously mentioned, tubular carcinoma is often admixed
(8). When present, nodal metastases from classic tumors usually also have a
cribriform structure while those derived from mixed tumors are more likely to have a
less well-differentiated noncribriform pattern (6,7).
Calcifications are reportedly found microscopically in at least 50% of tubular
carcinomas. They may be distributed in the neoplastic glands or in the stroma but are
most often found in the intraductal carcinoma component, which has been described in
60% to 84% of tubular carcinomas (4,11,18,19). It is possible to find intraductal
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