An Immunohistochemical Algorithm to Facilitate Diagnosis and Subtyping of Rhabdomyosarcoma: The Childrenʼs Oncology Group Experience

Abstract

Immunohistochemistry remains the current ancillary method of choice in the pathologic evaluation of small blue round-cell tumors. In at least 20% of cases of rhabdomyosarcoma (RMS), it is considered an essential factor in the final and/or differential diagnosis of the malignancy. Newer immunostains (antimyogenin, MyoD1) generated against intranuclear myogenic transcription factors offer pathologists the best hope for improving the sensitivity and specificity of RMS diagnosis. A large series of RMS (956) were studied consecutively from the intergroup rhabdomyosarcoma study and children's oncology group files, along with multiple other malignant, benign or reactive lesions. A panel of antibodies to muscle-related antigens (myogenin, MyoD1, desmin, muscle-specific actin) was studied using formalin-fixed, paraffin-embedded tissue, an avidin-biotin/peroxidase complex immunohistochemical technique, antigen retrieval technique as appropriate, and automated immunostaining. Myogenin and MyoD1 were equally sensitive (positive for 97% of RMS cases), with both also showing similar specificity (90% vs. 91% of cases) for the diagnosis of RMS. Myogenin and MyoD1 staining were sometimes intact in areas of coagulative tumor necrosis, but negated by B5 fixation. Isolated, rare benign myogenin-positive nuclei were seen infrequently in reactive lymph nodes. Specifically, both myogenin and MyoD1 had significantly greater extent of expression for alveolar RMS (ARMS) than embryonal RMS (ERMS) (both with P < 0.001). Similarly, both myogenin (P = 0.001) and MyoD1 (P < 0.001) had significantly higher expression for ARMS than RMS, not otherwise specified (NOS). They were never expressed in undifferentiated sarcomas; however, reactive or regenerative myocytes did show expression. Immunostains against intranuclear myogenic transcription factors are, at present, the best available markers for confirming the diagnosis of RMS. Their differential expression in reactive myogenic lesions, variability in ARMS versus ERMS, and absence in undifferentiated sarcomas suggest new biologic questions to be explored in future studies.

Anaplastic lymphoma kinase status in rhabdomyosarcomas

“…Classic alveolar rhabdomyosarcoma is characterized by uniform cytology and a greater extent of myogenin staining compared with non-alveolar subtype. 25,33 Therefore, the presence of pleomorphic tumors and less extensive myogenin positivity in the ALK-negative alveolar cases may suggest that this subgroup includes non-classical examples. Some of these might be close to (or might actually represent) the non-alveolar subtype that is indistinguishable from alveolar rhabdomyosarcoma on the basis of morphological criteria alone.…”

“…All the tumors were positive for desmin and one or both of the myoregulatory proteins (myogenin and myoD1). 25 Of note, our study population predominantly included adults: 60% of the patients were Z18 years of age (median age, 20 years). All the tumors were reclassified on the basis of the latest World Health Organization scheme [1][2][3] and the recent literature, 4-7 into embryonal (n ¼ 33), alveolar (n ¼ 61), pleomorphic (n ¼ 8), adult-spindle-cell/sclerosing (n ¼ 12), and epithelioid rhabdomyosarcomas (n ¼ 2).…”

Sarcomas induced in discrete subsets of prospectively isolated skeletal muscle cells

“…STS vary clinically and histopathologically (1,2), and this heterogeneity may result from differences in the lineage commitment and differentiation state of the sarcoma cell-of-origin, from genetic or epigenetic changes that occur during transformation, or from a combination of these factors (3). Sarcomas with myogenic features constitute the large and varied category of rhabdomyosarcomas (RMS) (4,5), for which satellite cells (6,7), more differentiated muscle-lineage cells (3,8), and undifferentiated mesenchymal cells (9) have been discussed as putative cells-of-origin. Still, the network of cellular and molecular events driving sarcomas in muscle is largely unknown (10).…”

How Our Practice of Histopathology, Especially Tumour Pathology has Changed in the Last Two Decades: Reflections from a Major Referral Center in Pakistan

“…Apart from vimentin (which in poorly differentiated cases often helped to determine that a neoplasm was mesenchymal in origin or not), the IHC markers which proved very useful to us in the early years, included desmin, actin, CD68, S100 protein, CD99 (MIC2) etc. This panel was greatly strengthened after 2000 by the additional of several useful markers including CD 34 in vascular neoplasms (Miettinen et al, 1994) and solitary fibrous tumor (SFT) (Nielsen et al, 1997); cytokeratin 19 in epithelioid sarcoma (Miettinen et al, 1999); CD34 in dermatofibrosarcoma protuberans (DFSP) (Mentzel et al, 1998); EMA and cytokeratin 19 in synovial sarcoma Olsen et al, 2006); CD31 in vascular neoplasms (DeYoung et al, 1995); Myo D1 in rhabdomyosarcoma (Cessna et al, 2001;Morotti et al, 2006) etc. In the last five years, we have begun to recognize and diagnose newer entities like myxofibrosarcoma (Mentzel et al, 2013;WHO, 2013) and low grade fibromyxoid sarcoma (Folpe et al, 2013;WHO, 2013).…”