Invasive breast carcinoma - IARC

A
B
Fig. 1.97 Microinvasive carcinoma. A Two ducts are filled by DCIS, while small clusters of carcinoma cells invade the stroma (upper right quadrant of the field)
admixed with a dense lymphocytic infiltrate. B Higher magnification shows small invasive cell clusters within stromal spaces distributed over a 0.7 mm area and
surrounded by a dense lymphocytic infiltrate. C Immunostain for actin decorates the vessel walls, while absence of myoepithelial cells around the tumour cell clusters
confirms their invasive nature.
C
the specialized lobular stroma and
immediately surrounding the basement
membrane that invests the ducts.
Associated lesions
Ty p i c a l l y, microinvasive carc i n o m a
occur in larger areas of high grade DCIS
in which the tumour cell population
extends to involve lobular units or are a s
of benign disease.
M i c roinvasion occurs in association not
only with all grades of DCIS, including
p a p i l l a ry DCIS, but also with other precursor
lesions of invasive breast cancer,
e.g. lobular neoplasia (LN) {1226,1249,
1993}, indicating that at least some
f o rms of lobular neoplasia behave as
true precursors of invasive lesions.
S t romal re a c t i o n
M i c roinvasion is most often present in
a background of significant periductal /
perilobular lymphocytic infiltrate or an
a l t e red desmoplastic stroma, feature s
often present in cases of comedo DCIS.
Angulation of mesenchymal structure s
may be emphasized by the plane of
sectioning and can produce feature s
reminiscent of invasive carc i n o m a .
Basement membrane structures in such
foci may be discontinuous but it is
unusual to lose the entire basement
membrane around such a lesion.
Similarly myoepithelial cells may be
s c a rce but are rarely totally absent in
such are a s .
Change in morphology
When true invasion extends into nonspecialized
stroma, the islands of
tumour cells frequently adopt a diff e re n t
morphological character which is more
typical of well established invasive
m a m m a ry carcinoma of ductal NOS
type and is distinct from the pattern s
seen with cancerization of lobules.
Differential diagnosis
When there is doubt about the presence
of invasion and particularly, if uncertainty
persists even after recuts and immunostains
for detection of myoepithelial cells,
the case should be diagnosed as an in
situ carcinoma. Similarly, suspicious
lesions which disappear on deeper levels
should be regarded as unproven,
with no definite evidence of established
invasion.
Invasion is associated with a loss of
immunoreactivity to myoepithelial cells. A
variety of markers is available for the
identification of myoepithelial cells
{3181}. The most helpful include smooth
muscle actin, calponin, and smooth muscle
myosin (heavy chain); the latter in
particular shows the least cross-reactivity
with myofibroblasts that may mimic a
myoepithelial cell layer when apposed to
the invasive cells.
Prognosis and predictive factors
In true microinvasive carcinomas of the
breast, the incidence of metastatic disease
in axillary lymph nodes is very low
and the condition is generally managed
clinically as a form of DCIS.
However, given the lack of a generally
accepted standardized definition of
microinvasive carcinoma, there is little
evidence on the behaviour of microinvasive
carcinoma. A recent detailed review
of the literature {2425} concluded that a
variety of different diagnostic criteria and
definitions have been used and as a consequence
it is difficult to draw any definitive
conclusions.
There are studies that have found no evidence
of axillary node metastases associated
with a finite number of invasive
foci