Invasive breast carcinoma - IARC

eadily recognizable. The tumours range
in size from less than 1 cm to over 20 cm,
with an average of 2.8 cm {1498,2338,
2447,2934}.
A
Mucin producing carcinomas
Definition
A variety of carcinomas in the breast are
characterized by production of abundant
extracellular and/or intracellular mucin.
Among these are mucinous (colloid) carcinoma,
mucinous cystadenocarcinoma,
columnar cell mucinous carcinoma and
signet ring cell carcinoma.
Mucinous carcinoma
Mucinous carcinoma is characterized by
a proliferation of clusters of generally
small and uniform cells floating in large
amounts of extracellular mucus often visible
to the naked eye.
B
C
Fig. 1.29 Mucinous carcinoma. A Mammogram showing small rounded density of less than 10 mm diameter
in the upper-outer quadrant. B Ultrasound suggests mucinous carcinoma. C Low power view of the
mucinous carcinoma.
Fig. 1.30 Mucinous carcinoma. 38 year old patient,
tumour excision.
ICD-O code 8480/3
Synonyms
Colloid carcinoma, mucoid carcinoma,
gelatinous carcinoma.
Epidemiology
Pure mucinous carcinoma accounts for
about 2% of all breast carc i n o m a s
{2338,2590,2934}. It occurs in a wide
age range, but the mean and median
age of patients with mucinous carcinoma
in some studies is somewhat higher than
that of regular infiltrating carc i n o m a s ,
being often over 60 years {2447,2590}.
Clinical features
The tumours usually present as a palpable
lump. The location is similar to
that of breast carcinomas in general.
Mammographically, mucinous carcinoma
appears as a well defined, lobulated
lesion. On magnification or compre s s i o n
views {547}, a less defined margin
may become more evident. The mammographic
resemblance to a benign
process (circumscription and lobulation)
increases with increasing mucin content.
Macroscopy
The typical glistening gelatinous appearance
with bosselated, pushing margins
and a soft consistency make the lesion
Histopathology
Mucinous carcinoma is characterized by
proliferation of clusters of generally uniform,
round cells with minimal amounts of
eosinophilic cytoplasm, floating in lakes
of mucus. Delicate fibrous septae divide
the mucous lake into compartments. The
cell clusters are variable in size and
shape; sometimes with a tubular
arrangement; rarely, they assume a papillary
configuration. Atypia, mitotic figures
and microcalcifications are not common,
but occur occasonaly. An intraepithelial
component characterized by a micropapillary
to solid pattern is present in
30-75% of the tumours. The lakes of
mucin are mucicarmine positive, but
intracytoplasmic mucin is rarely present.
A notable proportion of the lesions have
neuroendocrine differentiation {150,855}
easily demonstrable by Grimelius stain or
immunoreaction for chromogranin and
synaptophysin (see also neuroendocrine
carcinoma of breast).
The descriptive term cellular mucinous
c a rcinoma has been used by some
{1751} to differentiate the endocrine variant
of mucinous carcinoma from the nonendocrine
one; presence of intracytoplasmic
neuroendocrine granules does
not always correlate with the degree of
cellularity, however.
Tr a d i t i o n a l l y, pure and mixed variants
of mucinous carcinoma have been
described {1498,2934}. A pure tumour
must be composed entirely of mucinous
carcinoma. The pure mucinous carcinomas
are further subdivided into cellular
and hypocellular variants. The former is
m o re likely to have intracytoplasmic
mucin and argyrophilic granules. As
soon as another pattern becomes evident
as a component of the tumour
mass, the lesions qualifies as a mixed
tumour (the proportion of the different
components should be noted). The most
common admixture is with regular invasive
duct carcinoma.
Differential diagnosis
The two lesions most likely to be confused
with mucinous carcinoma are myxoid
fibroadenoma and mucocoele like
lesion {2417}. The presence of compressed
spaces lined by epithelial and
30 Tumours of the breast