Invasive breast carcinoma - IARC

A
Fig. 1.153 Periductal stroma sarcoma, low grade. A An infiltrative hypercellular spindle cell proliferation surrounds ducts with open lumens. B At higher magnification,
the neoplastic spindle cells contain at least three mitotic figures per 10 high power fields.
B
p rocesses may be found in intracanalicular
FAs with hypocellular and oedematous
stroma, but the leaf-like pro c e s s e s
a re few in number and often poorly
f o rm e d .
The term giant FA as well as juvenile (or
cellular) FA have often been used inapp
ropriately as a synonym for benign PT.
Although the term periductal stro m a l
s a rcoma has been used as a synonym
for PTs {2079}, it is better restricted to a
v e ry rare non circumscribed biphasic
lesion characterized by a spindle cell
p roliferation localized around tubules
that retain an open lumen and absence
of leaf-like processes {2876}. These
often low grade lesions may recur and
r a rely pro g ress to a classic PT.
Malignant PTs may be confused with
p u re sarcomas of the breast. In such
case, diagnosis depends on finding
residual epithelial structures. However,
the clinical impact of these two entities
appears to be similar {1887}.
G r a d i n g
Several grading systems have been
p roposed with either two subgro u p s
{1596,2876}, or three subgroups {1473,
1887}. None is universally applied since
p rediction of the behaviour remains difficult
in an individual case.
Grading is based on semi-quantitative
assessment of stromal cellularity, cellular
pleomorphism, mitotic activity, margin
appearance and stromal distribution.
Because of the structural variability of
P Ts, the selection of one block for every
1 cm of maximal tumour dimension is
a p p ropriate {2876}. PTs should be subclassified
according to the areas of
highest cellular activity and most florid
a rchitectural pattern. The diff e re n t
t h resholds of mitotic indices vary substantially
from author to author. Since
the size of high power fields is variable
among diff e rent microscope brands, it
has been suggested that the mitotic
count be related to the size of the field
diameter {1887}. Stromal overgro w t h
has been defined as stromal pro l i f e r a-
tion to the point where the epithelial elements
are absent in at least one low
power field (40x) {3058}. So defined,
s t romal overgrowth is not uncommon.
Table 1.18
Main histologic features of the 3 tiered grading subgroups for phyllodes tumours.
Benign Borderline Malignant
Stromal hypercellularity modest modest marked
Cellular pleomorphism little moderate marked
Mitosis few if any intermediate numerous (more
than 10 per 10 HPF)
Margins well circumscribed, intermediate invasive
pushing
Stromal pattern uniform stromal heterogeneous marked stromal
distribution stromal expansion overgrowth
Heterologeous stromal rare rare not uncommon
differentiation
Overall average 60% 20% 20%
distribution {1887}
Prognosis and predictive factors
Local recurrence occurs in both benign
and malignant tumours. Recurrence may
mirror the microscopic pattern of the
original tumour or show dedifferentiation
(in 75% of cases) {1067}. Metastases to
nearly all internal organs have been
reported, but the lung and skeleton are
the most common sites of spre a d .
Axillary lymph node metastases are rare,
but have been recorded in 10-15% in
cases of systemic disease {1887,2876}.
Recurrences generally develop within 2
years, while most deaths from tumour
occur within 5 years of diagnosis, sometimes
after mediastinal compre s s i o n
through direct chest wall invasion.
The frequency of local recurrence and
metastases correlate with the grade of
P Ts but vary considerably from one
series to another. The average in pub-
102 Tumours of the breast