Invasive breast carcinoma - IARC

cases, anisokaryosis has no prognostic
implication The behaviour of dysgerminoma
with trophoblastic differentiation is
identical to the usual type, but with the
advantage of having β-hCG as a serum
marker.
Yolk sac tumour
Definition
Yolk sac tumours are morphologically
h e t e rogeneous, primitive teratoid neoplasms
differentiating into multiple endodermal
structures, ranging from the primitive
gut to its derivatives of extraembryonal
(secondary yolk sac vesicle) and
embryonal somatic type, e.g. intestine,
liver {2035}. These neoplasms have
many epithelial patterns and are typically
immunoreactive for alpha-fetoprotein.
Synonym and historical annotation
Since the secondary yolk sac component
represents only one of its many lines of
differentiation, the current nomenclature
is clearly restrictive. Perhaps the term
“endodermal primitive tumours” would
be more accurate in defining all the possible
lines of differentiation, both epithelial
and mesenchymal, that occur in
these neoplasms.
The term “endodermal sinus tumour”,
although still in use, is misleading, since
the endodermal sinus is neither a structure
present in human embryogenesis
{1463} nor is it a constant feature of these
neoplasms, as it only occurs in a minority
of cases {1537}.
Macroscopy
These tumours are usually well encapsulated
with an average diameter of 15 cm
{1537}. The sectioned tumour surface is
soft and grey-yellow with frequent areas
Fig. 2.89 Yolk sac tumour. Sectioned surface is predominately
solid and fleshy with areas of haemorrhage,
necrosis and cyst formation.
Table 2.05
Morphological patterns of yolk sac tumours with their equivalent types of tissue differentiation.
Site differentiated Tissue differentiated Histological pattern
Extraembryonal endoderm
Somatic endoderm
Primitive endoderm and
secondary yolk sac
Allantois
Murine-type (?) parietal
yolk sac
of necrosis, haemorrhage and liquefaction.
Cysts can be found in the periphery
f o rming a honeycomb appearance
{2043}; rare l y, they can be unicystic
{522}. A relatively frequent finding is the
presence of a benign cystic teratoma in
the contralateral ovary {3033}.
Histopathology
Although a marked histological heterogeneity
due to numerous patterns of differentiation
coexisting in the same neoplasm
may occur, almost invariably characteristic
areas are present that allow for
the correct diagnosis.
The characteristic reticular pattern
formed by a loose, basophilic, myxoid
stroma harbouring a meshwork of microcystic,
labyrinthine spaces lined by clear
or flattened epithelial cells with various
degrees of atypia and cytoplasmic PASpositive,
diastase-resistant hyaline globules
permits tumour identification.
Irregular but constant amounts of hyaline,
amorphous basement membrane
material are found in relation to the
epithelial cells. Both hyaline globules
and the coarse aggregates of basement
membrane material {2032,2979} are
good histological indicators for tumour
identity. Less frequently, in 13-20% of
cases, papillary fibrovascular projections
lined by epithelium (Schiller-Duval bodies)
are found that bear a resemblance to
the structures of the choriovitelline placenta
of the rat, a fact that permitted the
establishment of the teratoid, endodermal
identity of these tumours {2896}.
Histological variants
Less common histological variants
include the polyvesicular vitelline tumour,
solid yolk sac tumour, parietal yolk sac
Primitive intestine and lung (?)
Early liver
Reticular
Solid
Endodermal sinus
Polyvesicular
Parietal
Glandular
Hepatic
t u m o u r, glandular types of yolk sac
tumour and hepatoid yolk sac tumour.
In the polyvesicular vitelline tumour cystic,
organoid change of the epithelial
spaces occurs that consists of multiple
dilatations lined by mesothelial-like cells
that coexist with a columnar, PAS-positive
epithelium {2043}.
The solid yolk sac tumour shows areas of
solid epithelial sheets of cells with a characteristic
abundant clear cytoplasm and
numerous hyaline globules. These areas
may resemble anaplastic changes of
d y s g e rminoma or even clear cell
tumours {1537} but have the distinctive
immunophenotype of a yolk sac tumour.
Although exceptionally rare, parietal-type
yolk sac tumours that are AFP-negative
have been described {598,620}. They
a re analogous to the experimental
murine tumour of the same name and
can be identified by the massive deposition
of amorphous extracellular basement
membrane, a material similar to the
Reichert membrane of the murine parietal
yolk sac.
D i ff e rentiation into organized somatic
endodermal derivatives such as endodermal
type gland-like structures resembling
early lung and intestine as well as
liver tissue can occur in a focal fashion in
as many as a third of tumours {1968,
2515,2979}. In rare instances these differentiated
tissues may become the predominant
elements in the tumour.
Extensive differentiation of endodermal
type glands characterizes the glandular
variants of yolk sac tumours, which may
adopt different morphological subtypes.
F rom an embryological viewpoint the
more immature type is represented by
n u m e rous dilated angular glands or
papillae lined by an eosinophilic colum-
Germ cell tumours 165