Ductal Carcinoma
In Situ
389
FIG. 11.73.
Invasive ductal carcinoma with DCIS pattern.
A:
Extensive carcinoma with this appearance in the breast
was interpreted as DCIS. Immunostains revealed absence
of myoepithelial cells and basement membrane around
some glandular structures, indicative of an invasive com-
ponent.
B,C:
Metastatic carcinoma in ALNs duplicated the
DCIS-like appearance of the primary invasive tumor.
It is essential to use more than one immunostain, since
reactivity is not equally intense with all reagents.
2. The absence of demonstrable immunoreactivity with
an appropriate marker usually means that myoepithe-
lial cells are not present, although they can be severely
attenuated and difficult to recognize. Loss of the myo-
epithelial cell layer occurs in some but not all DCIS and
in certain types of benign (e.g., cystic apocrine lesions)
and noninvasive neoplastic (e.g., some forms of papil-
lary) processes. By itself, absence of myoepithelial cells
is not indicative of invasive carcinoma, and the interpre-
tation of this finding depends on the assessment of all
histologic appearances of the lesion in the corresponding
H&E section.
3. A
new
consecutive H&E section must be prepared
whenever immunostains are done for suspected mi-
croinvasion. This is necessary because the structure
of the lesional tissue changes as additional slides are
made.
4. Cytokeratin immunostains are essential for the evalua-
tion of any focus suspected to be the site of microinva-
sion. It is recommended that at least two different stains
be used (e.g., CK7 and AE1/3) because of the variable
reactivity of carcinoma cells. Cytokeratin immunostain-
ing highlights the distribution of epithelial cells and dis-
tinguishes epithelial cells from histiocytes.
5. Immunostains for basement membrane components,
laminin and type IV collagen, are sometimes helpful.
Absence of reactivity for both components indicates a
strong likelihood of invasive carcinoma, especially if
coupled with absence of myoepithelial cells. A reticulin
stain may also be helpful in this setting, as well as
whenever microglandular adenosis is a diagnostic
consideration.
6. Reactivity for one or both basal lamina components
in the absence of myoepithelial cells presents the most
difficult diagnostic situation that requires assessment
of the entire lesion, including multiple H&E levels if
possible (see #2). The presence of laminin and type IV
collagen favors a diagnosis of
in situ
carcinoma. How-
ever, consideration must be given to the possibility that
basal lamina may be formed at sites of invasion. With
presently available routine diagnostic techniques, the
distinction between basal lamina formed at sites of in-
vasion and basement membranes in
in situ
carcinoma
cannot be resolved with confidence in all cases.
It is recommended that the term microinvasion be used
for invasive lesions 1 mm or less in largest extent. This
definition has been adopted by the TNM staging system
with the rubric T1
mic
to provide a descriptive identity for
these unusually small invasive lesions that are otherwise
