Myogenin is a Specific Marker for Rhabdomyosarcoma: An Immunohistochemical Study in Paraffin-Embedded Tissues 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) specific marker for rhabdomyoblastic differentia- Myogenin belongs to a group of myogenic regula- tion. It gives consistent and easily interpretable re- tory proteins whose expression determines com- sults in routinely fixed tissues. mitment and differentiation of primitive mesenchy- mal cells into skeletal muscle. The expression of KEY WORDS: Myogenin, Rhabdomyosarcoma, myogenin has been demonstrated to be extremely Paraffin-embedded tissue, Immunohistochemistry. specific for rhabdomyoblastic differentiation, which Mod Pathol 2000;13(9):988–993 makes it a useful marker in the differential diagno- sis of rhabdomyosarcomas (RMS) from other malig- The differential diagnosis of rhabdomyosarcomas nant small round cell tumors of childhood. Com- (RMS) from other poorly differentiated pediatric mercially available antibodies capable of detecting round cell tumors, including the Ewing’s sarcoma myogenin in routinely processed formalin-fixed family of tumors (ESFT), neuroblastomas, and hema- paraffin-embedded (FFPE) tissue are now available. topoietic neoplasms can be difficult on histologic In this study, we evaluated myogenin expression grounds alone, although the use of an antibody panel using the monoclonal myf-4 antibody (Novocastra including mic-2, desmin, and hematopoietic lineage- Labs) on FFPE in a large number of pediatric tu- specific antibodies now allows an accurate diagnosis mors in order to define the clinical utility of this in the majority of cases. The expression of markers marker. A total of 119 tumors were studied. These specific for rhabdomyoblastic differentiation is partic- included 48 alveolar RMS (ARMS), 20 embryonal ularly useful in defining lineage in some poorly differ- RMS (ERMS), one spindle cell RMS, 16 Ewing’s sar- entiated/undifferentiated tumors and antibodies to comas (ES), six nephroblastomas, two ectomesen- MyoD1 and myogenin proteins have been found to chymomas, seven precursor hematopoietic neo- be of most use in this regard (1–5). Although staining plasms, five olfactory neuroblastomas, three for MyoD1 was the first to be used in the diagnostic neuroblastomas, six desmoplastic small round cell setting, nonspecific cytoplasmic staining often makes tumors, and five rhabdoid tumors. Distinct nuclear interpretation of results problematic when fixed tis- staining for myogenin was noted in all 69 RMS. sue sections are used (3, 6, 7). Antibodies to myf-4, the Notably, the number of positive tumor cells differed human homologue of myogenin, are also available between the ARMS and ERMS. In ARMS, the major- and have been evaluated in a few studies (3, 6–8). ity of tumor cells (75 to 100%) were positive, in However, these studies have included relatively few contrast to ERMS, in which the positivity ranged cases of RMS, particularly of alveolar subtype (3, 6, 8) ,from rare ؉ to 25% in all but three tumors. Addi- or are reported only in abstract form (6). In addition tionally, myogenin positivity was seen in two of two some have been performed only on frozen sections ectomesenchymomas and in two nephroblastomas (9). In this study, we report our findings with a new, with myogenous differentiation. All other tumors commercially available anti-myogenin antibody in a were clearly negative. Our results indicate that large series of RMS and other pediatric sarcomas to staining for myogenin is an extremely reliable and define the utility of this marker in the routine diag- nostic setting. Copyright © 2000 by The United States and Canadian Academy of Pathology, Inc. VOL. 13, NO. 9, P. 988, 2000 Printed in the U.S.A. MATERIALS AND METHODS 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- Cases were retrieved from the files of the Labora- ton, DC 20010-2970; fax: 202-884-4030. tory of Pathology, National Cancer Institute, National 988 Institutes of Health, Bethesda, Maryland and The nuclei staining positive: rare positive to 25%, 1ϩ;25 Johns Hopkins Hospital, Baltimore, Maryland. A total to 50%, 2ϩ;50to75%,3ϩ; and 75 to 100%, 4ϩ. of 119 tumors were evaluated, as summarized in Ta- ble 1. These included 69 cases of RMS (48 alveolar RESULTS subtype/ARMS; 20 embryonal subtype/ERMS; one spindle cell RMS) and 50 other tumors, consisting of Diagnosis was based on a combination of routine 16 ESFT, two ectomesenchymomas, six nephroblas- histologic and immunophenotypic criteria as well tomas, seven precursor hematopoietic neoplasms (in- as, in some cases, correlation with ultrastructural cluding four lymphoblastic lymphomas), six desmo- and molecular findings. The alveolar RMS were plastic small round cell tumors (DSRCT), five composed of nests of undifferentiated primitive- olfactory neuroblastomas (ONB), three neuroblasto- appearing small round blue cells in solid nests or mas/ganglioneuroblastomas (NB/GNB), and five rh- with a focal alveolar pattern. In some cases, cells abdoid tumors. Formalin-fixed paraffin-embedded with more abundant eosinophilic cytoplasm or (FFPE) blocks or unstained sections were available for multinucleated giant cell forms were evident. The all of the cases. Routine morphologic and immuno- PAX3/FKHR fusion transcript was detected in 16 of phenotypic studies were performed on 4-␮m thick 22 cases evaluated by RT-PCR. The embryonal RMS hematoxylin- and eosin-stained sections. Staining for were composed of round to spindled cells, often myogenin was also evaluated in a variety of fetal and with eosinophilic cytoplasm, arranged in compactly adult tissues (including skeletal muscle, heart, liver, cellular to more loose areas with a myxoid stroma. lung, kidney, gastrointestinal tract, spleen, lymph The results of staining for myogenin are summa- nodes, and brain). rized in Table 1. Nuclear staining for myogenin was Immunoperoxidase staining for myogenin was seen in all 48 ARMS (Fig. 1, 2, 3), 20 ERMS (Fig. 4), performed using the myf-4 antibody (L026, 1:10, as well as in the spindle cell RMS. The results of mouse monoclonal, Novocastra Labs, Burlingame, grading in the RMS cases are summarized in Table CA), according to the manufacturer’s recom- 2. Grade 4ϩ staining with 75 to 100% of nuclei mended protocol. Antigen retrieval was done in a staining positive was present in 44 ARMS, two cases pressure cooker for 40 min in 10 mM citrate buffer showed 3ϩ staining and in another two cases only with 0.1% Tween 20 at pH 6.0. Slides were incu- 20% of nuclei stained, consistent with 1ϩ staining. bated overnight with the primary antibody, fol- In contrast, in the ERMS group, 17 of 20 cases lowed by detection using standard protocol on an showed 1ϩ staining, with the number of positive automated immunostainer (Ventana Medical Sys- staining nuclei ranging from rare positive to 25%. In tems, Tuscon, AZ), according to the manufacturer’s three ERMS, staining was graded as 2ϩ, with 25 to instructions. Other immunoperoxidase stains in- 50% nuclei positive. None of the ERMS showed cluded actin (HHF35, ENZO, Farmingdale, NY), Grade 3ϩ or 4ϩ staining. The single case classified desmin (D33), Der 11, NSE, 12E7 (p30/32mic2) (all as spindle cell RMS showed 3ϩ staining. In 66 of the from DAKO, Carpinteria, CA), AE1/3 (Boehringer 69 RMS, desmin-stained slides were available for Mannheim, Indianapolis, IN), and S100 (Biogenex, review and all cases stained desmin-positive. In San Ramon, CA). some of the more primitive appearing ARMS, how- Staining for myogenin was graded from 1ϩ to 4ϩ ever, the number of myogenin-positive cells clearly as follows, based on the percentage of tumor cell exceeded the desmin positivity (Fig. 5). TABLE 1. Results of Immunostaining with myf-4 in Various Pediatric Tumors Diagnosis (# of Cases) myf-4 Rhabdomyosarcoma (69) 69/69ϩ Alveolar (48) 48/48ϩ Embryonal (20) 20/20ϩ Spindle cell (1) 1/1ϩ Other pediatric sarcomas (50) 0/50ϩ ESFT (16) 0/14ϩ Nephroblastoma (6) 2/6ϩa Ectomesenchymoma (2) 2/2ϩ DSRCT (6) 0/6ϩ Rhabdoid (5) 0/5ϩ Precursor hematopoeitic neoplasms (7) 0/7ϩ NB/GNB (4) 0/4ϩ Olfactory neuroblastoma (5) 0/5ϩ ESFT, Ewing’s sarcoma family of tumors; DSRCT, desmoplastic small round cell tumor; NB/GNB, neuroblastoma/ganglioneuroblastoma. FIGURE 1. Tumor cells with intense nuclear positivity infiltrate in a These two nephroblastomas had myogenous differentiation. solid nests as well as line spaces in an alveolar rhabdomyosarcoma. Myogenin Expression in RMS (S. Kumar, et al.) 989 FIGURE 2. A case of solid alveolar rhabdomyosarcoma with the FIGURE 4. Scattered but distinctly myogenin-positive cells in an majority of cells showing nuclear staining (4ϩ staining). embryonal rhabdomyosarcoma. Nuclei in some of the multinucleated rhabdomyoblasts are also positive. TABLE 2. Grading of Myogenin Expression in ARMS & ERMS Staining for myf-4 Diagnosis Grade 1 Grade 2 Grade 3 Grade 4 ARMS (48) 2 0 2 44 ERMS (20) 17 3 0 0 RMS, rhabdomyosarcoma; ARMS, alveolar RMS; ERMS, embryonal RMS. FIGURE 3. Staining for myf-4 in an alveolar rhabdomyosarcoma metastatic to the lymph node. Distinct nuclear positivity is seen in tumor cells within the subcapsular sinus whereas adjacent small lymphocytes are negative. Myogenin-positive cells were identified in the two ectomesenchymomas, correlating with the desmin positive areas. In one case, the majority of the tumor was composed of undifferentiated cells that expressed only mic-2, whereas, in focal areas, the mic-2 positive cells also co-expressed myoge- FIGURE 5. The number of tumor cells staining for myogenin (A) are nin, desmin and actin, as illustrated in Figure 6, more numerous than those marking with desmin (B) in a solid alveolar A-C. Staining for myogenin (as well as desmin) was rhabdomyosarcoma.