Ductal Carcinoma
In Situ
361
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.
FIG. 11.38.
DCIS in sclerosing adenosis.
Cribriform carci-
noma is present on the right. SA is present throughout the
photograph.
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
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
