384
Chapter 11
FIG. 11.66.
DCIS, basement membrane and microinvasion
.
A:
DCIS, comedo type with calcification (
right
) and micro-
invasive carcinoma (
left
).
B:
The immunostain for laminin
shows a multilayered basement membrane of variable
thickness. The basement membrane is incomplete in the
lower left
region, which is adjacent to the microinvasive
carcinoma shown in a parallel section in
(A)
.
C:
The immu-
nostain for CD34 shows maximal periductal neovascular-
ity on the
left
in the region of microinvasion.
than 1.0 cm in diameter.
289–291
Microinvasive carcinoma is a
subcategory of minimally invasive carcinoma. Microinvasion
is defined as an invasive focus 1 mm or less in greatest extent.
A controversial aspect of the histologic diagnosis of mi-
croinvasion relates to the interpretation of ducts that have
poorly defined walls with an indistinct basement membrane.
In such regions, the neoplastic epithelium may appear to
protrude from the duct wall, seeming to come in direct con-
tact with the stroma although it remains connected with the
intraductal neoplasm
292
(Figs. 11.29 and 11.67). This find-
ing often elicits diagnostic uncertainty reflected in such ca-
veats as “suspect microinvasion” or “microinvasion cannot
be ruled out.” Retrospective studies have given no indication
that these ambiguous findings are associated with an appre-
ciable risk of systemic metastases, but they may account for
some instances in which micrometastases have been detected
in sentinel lymph nodes (SLNs) from patients with DCIS.
To qualify for the term
microinvasion
, the cells deemed
to be invasive must be distributed in a fashion that does not
represent tangential sectioning of a duct or a lobular gland
with DCIS (Figs. 11.67 and 11.68). Tangentially sectioned
in
situ
carcinoma that simulates microinvasion usually results
in compact groups of tumor cells that have a smooth border
surrounded by a circumferential layer of cells of stromal and/
or myoepithelial origin. These “organoid” foci are distributed
in the specialized periductal or intralobular stroma. Immu-
nostains may be helpful in resolving the problem.
The choice of an immunohistochemical marker for myoep-
ithelial cells “should be dependent on a combination of factors,
including published evidence of its diagnostic utility, its avail-
ability, performance characteristics that have been achieved in
a given laboratory, and the specific diagnostic criteria.”
293
The markers or myoepithelium that are commonly de-
tected by immunostain in diagnostic pathology include the
following, in alphabetical order:
Calponin
inhibits ATPase activity of myosin in mammary
myoepithelial cells, wherein it is highly sensitive but not specific as
it is reactive in a subset ofmyofibroblasts.
CD10
is an endopeptide
that is relatively sensitive for the detection of myoepithelial cells.
CKs
5, 10, 14, and 17 are expressed in myoepithelial cells.
CK-K903 (34βE12) is not specific formyoepithelial cells, but is
useful for the diagnosis of metaplastic spindle cell carcinoma.
H-caldesmon
is an SMA-binding protein expressed in
myoepithelial cells, mainly around ducts.
Maspin
is a serine protease inhibitor, which is expressed
in the cytoplasm and nuclei of myoepithelial cells.
P-cadherin
is a cell adhesion molecule with high sen-
sitivity for myoepithelial cells, which is not reactive in
myofibroblasts.
p63
, a p53 homolog, is highly sensitive for myoepithelial
cells and is expressed in nuclei thereof.
S-100 protein
can be identified in a proportion of benign
and malignant mammary epithelial cells, as well as myoepi-
thelial cells, and therefore is not useful.
