10
June 2005 – Case of the Week #10
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This
week’s case is sponsored by Invitrogen. The Zymed® EGFr antibody clone
31G7 is the
most widely referenced clone and the industry standard for EGFr detection in formalin-fixed,
paraffin embedded (FFPE) tissue samples. Zymed’s 31G7 antibody
is extremely specific for EGFr and does not react with the highly homologous
c-erbB-2 (HER2) protein. Invitrogen now offers the Zymed® 31G7 antibody clone as part of a convenient, standardized
immunohistochemical kit for the detection of EGFr protein expression in normal
and neoplastic tissue. Invitrogen’s
Zymed® EGFr Kit is compatible
with manual or
automated
immunostainers and offers the greatest flexibility with FFPE tissue samples. For more information, visit www.invitrogen.com/antibodies. Note:
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We
thank Dr. David Lucas, University of Michigan Hospitals,
Case of the Week #10
A 30
year old man presented with a mass in the inner thigh. MRI disclosed an enhancing, heterogeneous
mass in the thigh, abutting the femur (image
#1). Following open biopsy, he was treated with adriamycin-based
chemotherapy, and the tumor was resected.
Grossly, it was largely gelatinous, but had areas that appeared fleshy (image
#2). Eighteen months later he
developed recurrent disease in the groin, and he ultimately died of
disseminated disease.
Micro
images (post-chemotherapy): image
#3; #4
Micro
description: The tumor showed variation from field to field. Some of the tumor was relatively hypocellular
with myxoid stroma, low grade nuclear cytology, plexiform small vascular
pattern, and readily identified signet ring type lipoblasts (image #3). However, most of the tumor was more cellular,
consisting of closely-spaced, overlapping, anaplastic round cells with scant
cytoplasm and readily identifiable mitotic activity. These areas had very little stroma, and much
fewer lipoblasts (image #4).
What
is your diagnosis?
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Diagnosis: High
grade myxoid / round cell liposarcoma
Discussion
Myxoid and round cell liposarcomas, although histologically
different, actually represent two ends of a spectrum for a tumor which almost
always has the same translocation, t(12;16)(q13;p11). They are common, and together account for 50%
of all liposarcomas. Tumors with pure
myxoid features are considered to be well differentiated, and to have a good
prognosis. However, round cell features
are considered high grade or poorly differentiated, and are associated with a
poorer outcome, even if they represent as little as 5% of the tumor
volume. Thus, apparent myxoid
liposarcomas should be sampled thoroughly to ensure that no significant round
cell component is present. This is a
particular problem with needle biopsies, which may entirely miss the round cell
component.
Myxoid/round cell liposarcomas frequently
metastasize, based in part on the percentage of round cells, with rates varying
from 23% (0-5% round cells) to 58% (>25% round cells). They metastasize to lung and bone, as well as
to other soft tissue sites.
Histologically, pure myxoid liposarcomas resemble
developing fetal adipose tissue, with a multinodular mass of low cellularity,
particularly centrally. The tumor cells
are bland, spindled or round, and lie within a myxoid matrix. Numerous lipoblasts are present, with one or
many vacuoles. There are no/rare mitotic
figures. A delicate plexiform
vasculature is present, and helps differentiate this tumor from myxoma.
The round cell component is often separated from the
myxoid component by a cellular transition area.
The round cells are primitive, with minimal eosinophilic cytoplasm, a
high N/C ratio, and prominent nucleoli.
Lipoblasts are less frequent than in myxoid areas. Often the cells are packed together with
minimal stroma, and blood vessels are difficult to find.
As noted, almost all myxoid/round cell liposarcomas
share a common t(12;16)(q13;p11) translocation resulting in the TLS-CHOP fusion
gene. Less common is t(12;22)(q13;p11)
or an insertion between chromosomes 12 and 16, (12;16)(q13;p11.2p13).
References: Weiss:
Enzinger and Weiss’s Soft Tissue Tumors; 2001 (4th edition), AJSP
1996;20:1047, AJSP
1996;20:171, Cancer
1996;15;77:1450
Nat
Pernick, M.D.
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