Invasive breast carcinoma - IARC

1113,1275}. There is a complex pattern of
interanastomosing empty slit-like spaces,
p resent within and between breast l o b-
ules with a perilobular concentric arrangement
{1275,2279}. In gynaecomastia, a
periductal pattern is found {157}. The
spaces are formed by separation of collagen
fibres and are either acellular or
lined by spindle cells, simulating endothelial
cells. Mitoses, tufting, atypia and
pleomorphism are absent {92,1275,2279,
3037,3249}. There is no destruction of
n o rmal breast tissue, no necrosis, nor
invasion of fat {1275} and collagen IV
cannot identify a basement membrane
a round the spaces {867}. The intervening
s t roma often consists of dense, hyalinized
collagen and spindle cells with
nuclei displaying pointed ends {1275,
2510}. In rare more proliferative lesions, a
fascicular pattern is found: the stroma is
composed of bundles of plump spindle
cells that may obscure the underlying
pseudoangiomatous arc h i t e c t u re {2279}.
At low power, PASH may resemble lowgrade
angiosarcoma but can be distinguished
by its growth pattern and cytological
features. The immunohistochemical
characteristics are also different.
Fig. 1.134 Myofibroblastoma. An expansile tumour composed of spindle to oval cells arranged in intersecting
fascicles interrupted by thick bands of collagen. Some adipose tissue is present in the right upper corner.
Immunoprofile
The spindle cells adjacent to the clefts are
positive for CD34, vimentin, actin, calponin,
but negative for the endothelial cell markers
Factor VIII protein, Ulex euro p a e u s
agglutinin-1 and CD31. They are also negative
for S100, low and high MW cytokeratins,
EMA and CD68. Desmin is usually
negative, but may be positive in fascicular
lesions {157,928,1865,2279,3037}.
Prognosis and predictive factors
PASH is not malignant but local re c u r re n c e
has been rarely re p o rted possibly attributable
to growth after incomplete excision,
or the presence of multiple lesions that
w e re not all excised {2270,2279,3037}.
Myofibroblastoma
Definition
A benign spindle cell tumour of the mamm
a ry stroma composed of myofibro b l a s t s .
ICD-O code 8825/0
Epidemiology
Myofibroblastoma (MFB) occurs in the
breast of both women and men aged
Fig. 1.135 Myofibroblastoma. A more epithelioid cell population may develop focally.
between 40 and 87 years {1023,1735}. In
a few cases, an association with gynaecomastia
has been documented.
Clinical features
MFB presents as a solitary slowly growing
nodule. Synchronous bilaterality and
unilateral multicentricity is rare l y
observed {1113}. Imaging shows a well
c i rcumscribed, homogeneously solid
and hypoechoic mass devoid of microcalcifications
{1113,1374,2252}.
Macroscopy
MFB is usually a well circ u m s c r i b e d
encapsulated tumour raging in size from
0.9 to 10 cm.
Histopathology
An expansile tumour with pushing borders,
myofibroblastroma is composed of
spindle to oval cells arranged in short,
haphazardly intersecting fascicles interrupted
by thick bands of brightly eosinophilic
collagen. The cells have relatively
abundant, ill defined, pale to deeply
eosinophilic cytoplasm with a round to
oval nucleus containing 1 or 2 small
nucleoli. Necrosis is usually absent and
mitoses are only rarely observed (up to 2
mitoses x 10 high power fields). There is
no entrapment of mammary ducts or lobules
within the tumour. Variable numbers
of scattered mast cells may be seen in
the stroma but otherwise inflammatory
Mesenchymal tumours
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