Myogenin is a Specific Marker for Rhabdomyosarcoma:
An Immunohistochemical Study in Paraffin-Embedded
S. Kumar, M.D., E. Perlman, M.D., C.A. Harris, B.Sc., M. Raffeld, M.D., M. Tsokos, M.D.
Laboratory of Pathology, National Cancer Institute, National Institutes of Health, Bethesda Maryland (SK,
CAH, MR, MT), and Johns Hopkins Hospital, Baltimore, Maryland (EP)
Myogenin belongs to a group of myogenic regula-
tory proteins whose expression determines com-
mitment and differentiation of primitive mesenchy-
mal cells into skeletal muscle. The expression of
myogenin has been demonstrated to be extremely
specific for rhabdomyoblastic differentiation, which
makes it a useful marker in the differential diagno-
sis of rhabdomyosarcomas (RMS) from other malig-
nant small round cell tumors of childhood. Com-
mercially available antibodies capable of detecting
myogenin in routinely processed formalin-fixed
paraffin-embedded (FFPE) tissue are now available.
In this study, we evaluated myogenin expression
using the monoclonal myf-4 antibody (Novocastra
Labs) on FFPE in a large number of pediatric tu-
mors in order to define the clinical utility of this
marker. A total of 119 tumors were studied. These
included 48 alveolar RMS (ARMS), 20 embryonal
RMS (ERMS), one spindle cell RMS, 16 Ewing’s sar-
comas (ES), six nephroblastomas, two ectomesen-
chymomas, seven precursor hematopoietic neo-
neuroblastomas, six desmoplastic small round cell
tumors, and five rhabdoid tumors. Distinct nuclear
staining for myogenin was noted in all 69 RMS.
Notably, the number of positive tumor cells differed
between the ARMS and ERMS. In ARMS, the major-
ity of tumor cells (75 to 100%) were positive, in
contrast to ERMS, in which the positivity ranged
from rare ? to 25% in all but three tumors. Addi-
tionally, myogenin positivity was seen in two of two
ectomesenchymomas and in two nephroblastomas
with myogenous differentiation. All other tumors
were clearly negative. Our results indicate that
staining for myogenin is an extremely reliable and
specific marker for rhabdomyoblastic differentia-
tion. It gives consistent and easily interpretable re-
sults in routinely fixed tissues.
Paraffin-embedded tissue, Immunohistochemistry.
Mod Pathol 2000;13(9):988–993
WORDS: Myogenin, Rhabdomyosarcoma,
The differential diagnosis of rhabdomyosarcomas
(RMS) from other poorly differentiated pediatric
round cell tumors, including the Ewing’s sarcoma
family of tumors (ESFT), neuroblastomas, and hema-
topoietic neoplasms can be difficult on histologic
grounds alone, although the use of an antibody panel
including mic-2, desmin, and hematopoietic lineage-
specific antibodies now allows an accurate diagnosis
in the majority of cases. The expression of markers
ularly useful in defining lineage in some poorly differ-
entiated/undifferentiated tumors and antibodies to
MyoD1 and myogenin proteins have been found to
be of most use in this regard (1–5). Although staining
for MyoD1 was the first to be used in the diagnostic
setting, nonspecific cytoplasmic staining often makes
interpretation of results problematic when fixed tis-
human homologue of myogenin, are also available
and have been evaluated in a few studies (3, 6–8).
However, these studies have included relatively few
cases of RMS, particularly of alveolar subtype (3, 6, 8)
or are reported only in abstract form (6). In addition,
some have been performed only on frozen sections
(9). In this study, we report our findings with a new,
commercially available anti-myogenin antibody in a
large series of RMS and other pediatric sarcomas to
define the utility of this marker in the routine diag-
MATERIALS AND METHODS
Cases were retrieved from the files of the Labora-
tory of Pathology, National Cancer Institute, National
Copyright © 2000 by The United States and Canadian Academy of
VOL. 13, NO. 9, P. 988, 2000 Printed in the U.S.A.
Date of acceptance: April 6, 2000.
Address reprint requests to: Shimareet Kumar, M.D., Anatomic Pathology,
Children’s National Medical Center, 111 Michigan Avenue, NW, Washing-
ton, DC 20010-2970; fax: 202-884-4030.
cell tumors evaluated in this study were clearly
negative for myogenin as expected.
Although our study did not include spindle cell
sarcomas or tumors such as alveolar soft part sar-
coma, recent studies have reported these tumors to
be consistently negative for myogenin (6, 7, 21). The
results of these studies are summarized in Table 3,
and, in conjunction with our large series, serve to
confirm the specificity of myogenin for rhab-
domyoblastic differentiation in the routine diag-
nostic setting. False positive results do not occur.
In conclusion, we find staining for myogenin to
be extremely sensitive and specific in defining rh-
abdomyoblastic lineage and a useful addition to the
diagnostic immunohistochemical panel for small
round blue-cell tumors. Although the literature sug-
gests that myogenin expression parallels that of
MyoD1, we believe that staining for the former is
definitely superior in terms of quality and ease of
interpretation. Furthermore, fixation does not ap-
pear to be a problem. The majority of our cases
were derived from consultation material, with an
inevitable variability in tissue fixation and process-
ing; however, good results were obtained in all
cases. Both ARMS and ERMS stain myogenin-
positive, although, clearly, the number of cells
staining in the latter subtype is fewer. This could be
a potential pitfall when only small biopsies or nee-
dle core specimens are being evaluated.
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Myogenin Expression in RMS (S. Kumar, et al.)993