Strong Immunostaining for Myogenin in Rhabdomyosarcoma Is Significantly Associated with Tumors of the Alveolar Subclass

Abstract

Rhabdomyosarcomas are a heterogeneous group of tumors with respect to their molecular basis, degree of differentiation, histology, and clinical behavior. Because of the wide variation of tumor morphology, it is often difficult to distinguish between the distinct subtypes of rhabdomyosarcomas. By using cryosections of tumor specimens and immunohistochemistry, in the present study we show that strong expression of myogenin in rhabdomyosarcoma is associated with alveolar histology (P ‫؍‬ <0.0001, Fisher's exact test). Although staining for myogenin was observed in 22 of 26 rhabdomyosarcomas, all alveolar rhabdomyosarcomas (nine of nine) showed high levels of staining for myogenin, as defined by the frequency and intensity of staining of the tumor cells. The staining pattern suggests that the tumor cells are clonally derived from myogenin-positive progenitor cells. In contrast, most embryonal rhabdomyosarcomas (13 of 15) were either negative or showed a low level of staining for myogenin. In these tumors a larger proportion of tumor cells were distinctly negative for myogenin. Six of seven alveolar rhabdomyosarcomas that strongly stained for myogenin were also positive for Pax3-7/Forkhead (FKHR) by polymerase chain reaction/reverse transcriptase-polymerase chain reaction. One of two embryonal rhabdomyosarcomas that strongly stained for myogenin was retrospectively found to be positive for Pax3/FKHR transcripts. Quantitative analysis for myogenin by Western blotting using a smaller subset of rhabdomyosarcomas revealed that in general there was a good correlation between immunohistochemical staining and Western blotting (P ‫؍‬ 0.01, Pearson Correlation), although the former technique was more sensitive for detecting tumors with low levels of the protein. On average, alveolar rhabdomyosarcomas expressed at least threefold more myogenin than embryonal rhabdomyosarcomas. Our data show that staining for myogenin will be a simple, rapid, and accurate adjunct for distinguishing between alveolar and embryonal rhabdomyosarcomas. We propose that embryonal rhabdomyosarcomas result from an early block in myogenesis, before the expression of myogenin. In contrast, we propose that alveolar rhabdomyosarcomas either originate from a late block in myogenesis (after expression of myogenin) or that the pathological mechanisms involved in these neoplasms also induce strong expression of this protein. Rhabdomyosarcomas are malignant myogenous tumors that can occur in any part of the body, including both skeletal muscle tissue and sites that are devoid of muscle. 1 These tumors are highly heterogeneous, not only with respect to their clinical behavior, but also with respect to the tumor morphology and spectrum of differen-

Pleomorphic Rhabdomyosarcoma in Adults: A Clinicopathologic Study of 38 Cases with Emphasis on Morphologic Variants and Recent Skeletal Muscle-Specific Markers

“…MyoD1 and the myogenins (including myf4 and myf3) belong to a family of closely related genes encoding a series of DNA binding proteins that are thought to control myogenesis (27,32,34). MyoD1 and myf4 were less sensitive for PRMS, in our experience.…”

“…MyoD1, the product of a gene activated early in myogenesis, was discussed as a skeletal muscle-specific marker but was not applied to pleomorphic rhabdomyosarcoma until 1995 (31-33). Myf4, a skeletal muscle-specific myogenin, has only been studied on four cases of PRMS in the literature (27,34). The current study reports 38 adult cases of PRMS, from the 1970s to the present, diagnosed by using a current morphologic and immunohistochemical approach, the latter aforementioned specific and nonspecific striated muscle markers.…”

Aberrant expression of epithelial and neuroendocrine markers in alveolar rhabdomyosarcoma: a potentially serious diagnostic pitfall

“…Beginning in the late 1980s, with the recognition of the utility of immunohistochemistry for muscle actins and desmin in the distinction of alveolar rhabdomyosarcoma from other primitive malignant neoplasms, and continuing in the 1990s with the advent of immunohistochemistry for first MyoD1 and subsequently myogenin, immunohistochemistry has assumed a primary role in the diagnosis of alveolar rhabdomyosarcoma. 15,[35][36][37] With increasing use of immunohistochemistry, however, has come the recognition that the expression of many markers may be considerably more widespread than was initially thought, with expression of desmin, for example, now well recognized in a variety of non-myogenic neoplasms, such as Ewing sarcoma/ primitive neuroectodermal tumor, 38 ossifying fibromyxoid tumor, 39 and angiomatoid (malignant) fibrous histiocytoma, 40 among others. Similarly, expression of putative epithelial markers, such as Epithelial and neuroendocrine markers in alveolar rhabdomyosarcoma A Bahrami et al cytokeratins, has now been recognized to occur in a variety of neoplasms apparently lacking epithelial differentiation, including angiosarcoma, 41 leiomyosarcoma, 42 Ewing sarcoma/primitive neuroectodermal tumor, 43 and schwannoma.…”

“…9,10 By immunohistochemistry, alveolar rhabdomyosarcomas typically express vimentin, desmin, muscle actins (including smooth muscle isoforms), myogenin, and MyoD1. [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] Myogenin and MyoD1, two of the myogenic transcriptional regulatory proteins, are highly sensitive and are specific markers of rhabdomyoblastic differentiation. 30,31 In general, myogenin expression is uniform and intense in alveolar rhabdomyosarcoma and somewhat more patchy and weak in embryonal rhabdomyosarcoma.…”

“…30,31 In general, myogenin expression is uniform and intense in alveolar rhabdomyosarcoma and somewhat more patchy and weak in embryonal rhabdomyosarcoma. 15 At the genetic level, alveolar rhabdomyosarcomas are characterized in nearly 80% of cases by one of two specific translocations, t(2;13)(q35;q14), found in approximately 60% of cases, or t(1;13)(p36;q14), found in approximately 20% of cases. 32,33 The t(2;13) results in fusion of the PAX3 gene on chromosome 2 to the FKHR (FOX-O1A) gene on chromosome 13, whereas the t(1;13) results in fusion of the PAX7 gene on chromosome 1 to the FKHR gene.…”