386
Chapter 11
FIG. 11.69.
DCIS with microinvasive carcinoma.
A:
Carci-
noma cells in groups and individually in reactive stroma
.
B:
Magnified view (of
box
in
[A]
) showing individual carci-
noma cells that were partially obscured by the inflamma-
tory reaction.
C:
Invasive carcinoma cells are highlighted
by this CAM5.2 immunostain for cytokeratin.
SMA
antibody detects actin filaments in myoepithelial
cells, but its specificity is poor since myofibroblasts are also
highlighted by SMA.
SMM-HC
detects structural smooth
muscle elements in mammary myoepithelial cells but not in
myofibroblasts.
185,293
It is notable that CD10 is expressed uniformly in myoepi-
thelial cells from the terminal duct to acini, and that caldes-
mon is immunoreactive in myoepithelial cells of large ducts,
but is not typically expressed in intralobular ductules and
acini.
294
In practical terms, SMM-HC and p63 are the most
useful immunostains for the diagnosis of microinvasive
carcinoma.
At sites of clear-cut microinvasive ductal carcinoma, tu-
mor cells are distributed singly or as small groups that have
irregular shapes reminiscent of conventional invasive carci-
noma with no particular orientation (Figs. 11.66 to 11.69).
Sometimes the intralobular or periductal stroma appears less
dense at sites of microinvasion than in other areas around
these structures. Detecting carcinoma cells in the stroma can
be difficult when there is a periductal and stromal inflamma-
tory cell reaction. Microinvasion may be suspected at sites
where there is a pronounced lymphocytic accumulation near
ducts with DCIS (Fig. 11.70). A granulomatous reaction may
be elicited at foci of microinvasion.
295
The tumor cells can
resemble histiocytes, and it may require immunostains for
cytokeratin to confirm the presence of microinvasion. Dou-
ble immunolabeling for cytokeratin and actin is an elegant
method for visualizing foci of microinvasion (Fig. 11.42).
296
Microinvasion is most often associated with high-grade
DCIS, but it may occur in other types of DCIS.
56
Thorough
histologic sectioning is recommended for all cases of high-
grade DCIS and for other types of DCIS that form a co-
hesive lesion larger than 2 cm. Serial routine H&E-stained
sections, supported by IHC, usually provide the best evi-
dence of microinvasion. Minimal trimming of the block,
with conservation of diagnostic tissue, should be ensured
in such cases. Care should also be taken to obtain immu-
nostains (including those for cytokeratin, myoepithelial
markers, and hormone receptors) early in the evaluation
of suspected microinvasion before the sample has been
excessively sectioned. At least one H&E slide must always
be prepared whenever immunostains are done to study a
specimen for microinvasion. Carcinomatous epithelium
displaced by needling procedures can usually be distin-
guished from intrinsic invasive carcinoma (Fig. 11.71).
The presence of minute clusters of carcinomatous epi-
thelial cells arranged in a linear manner, typically associ-
ated with granulation tissue, fat necrosis, and hemosiderin
