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Alveolar rhabdomyosarcoma (ARMS) is a distinct subtype of rhabdomyosarcoma. It usually arises in extremities and axial musculature.[1] These lesions affect all ages and are more common in adolescents and young adults, unlike other subtypes which are more common in childhood.[1],[2] Head and neck are uncommon sites of ARMS.[1] Alveolar rhabdomyosarcoma is extremely difficult to distinguish from other primitive round cell neoplasms without immunohistochemistry and/or genetic study. Expression of CD 56 is seen in 30–40% of ARMS.[2] We represent an unusual case of alveolar rhabdomyosarcoma with CD56 positivity which was diagnosed outside as extranodal NK/T cell lymphoma on flow-cytometry. CD56 is expressed in hematolymphoid and nonhematolymphoid neoplasm. Hematolymphoid neoplasm includes NK/T cell lymphoma, Myeloid sarcoma, Pediatric anaplastic large cell lymphoma, plasmacytoid dendritic cell neoplasm, gamma delta (γδ) T cells, and activated CD8+ T cells as well as on dendritic cells (DCs). Other nonhematolymphoid neoplasms include alveolar rhabdomyosarcoma, meningioma, pulmonary meningothelial-like nodules, Merkel cell carcinoma, Neuroblastoma (adult), neuroendocrine carcinomas, pancreatic neuroendocrine tumor, pheochromocytoma, synovial sarcoma, and Wilms tumor. However, we could establish an accurate diagnosis on careful observation of cytomorphological features and immunohistochemistry on cell blocks.
A 25-year-old female presented with a nasal mass with recent-onset exertional dyspnea and occasional epistaxis. She was diagnosed outside with extranodal NK/T cell lymphoma on flow-cytometry and was referred to our hospital for further treatment. On CECT PNS there was a soft tissue mass in the left anterior nasal cavity inseparable from the left-sided nasal turbinates, septum, and hard palate. CT guided fine needle aspiration cytology was done, as the material was too scant only cell blocks were made. H and E sections showed moderate cellularity and sheets of dyscohesive cells. These cells were small round cells having irregular hyperchromatic nuclei, inconspicuous nucleoli, and scant to moderate eosinophilic cytoplasm. Few mitotic figures were also seen. On immunohistochemistry these cells were positive for desmin, myogenin, myo D1, and CD 56. The cells were negative for LCA and cytokeratin. A diagnosis of alveolar rhabdomyosarcoma was rendered.
Cytologically alveolar rhabdomyosarcoma shows singly dispersed small blue round cells with occasional eccentric nuclei and abundant eosinophilic cytoplasm. Differential diagnosis includes malignant lymphoma, Ewings sarcoma, neuroblastoma, retinoblastoma, nephroblastoma, synovial sarcoma, and poorly differentiated carcinoma. However, it is difficult to make a definite diagnosis on cytological findings alone.[2],[3] On-site evaluation of these tumors on FNAC is difficult due to their resemblance to hematological malignancies. As a result, the aspirate undergoes immunophenotyping to exclude non-Hodgkin lymphoma (NHL). The strong positivity of CD 56 on immunophenotyping can lead to an erroneous diagnosis, as seen in our case. However, pathologists should be alerted by CD 45 negativity.
There are some differentiating cytomorphological features of NK/T cell lymphoma which differentiate alveolar rhabdomyosarcoma. The Cytomorphological feature of NK/T cell lymphoma is the hypercellular pattern with dyscohesive sheets of the polymorphous infiltration of the small, medium, and large atypical lymphocytes interspersed with plasma cells, macrophages, neutrophils, and occasional histiocytes. Cells show scant to moderate amounts of cytoplasm with pleomorphic nuclei and small nucleoli. These atypical cells are positive for CD 56 and CD 45 on cell block sections, while FNAC of rhabdomyosarcoma revealed dyscohesive sheets of small blue round cells with occasional eccentric nuclei and abundant eosinophilic cytoplasm [Figure 1]a,[Figure 1]b. Few cells are arranged in an alveolar pattern. Immunohistochemically, the tumor cells expressed CD56 but CD 45 negative [Figure 2]a, [Figure 2]b, [Figure 2]c, [Figure 2]d, [Figure 2]e, [Figure 2]f. Pathologists should be alerted by CD 45 negativity.
Cellblock of fine-needle aspiration from nasal mass shows the polymorphous population of tumor cells with eccentrically placed hyperchromatic nuclei with abundant eosinophilic cytoplasm. Mitosis also seen. (H and E; Magnification (a) x100 & (b) x 400)
[a-f] Immunocytochemistry; (a) CD56 showing membranous positivity; (b) desmin showing cytoplasmic positivity in large neoplastic cells; (c) myogenin showing diffuse and strong nuclear positivity; (d-e) Ki67 and myoD1 showing nuclear positivity; (f) CD 45 showing negative stainingWin KT et al.[4] reported a similar case of ARMS where the initial diagnosis of Extranodal NK/T cell lymphoma was made on flow-cytometry. Yasuda T et al.[5] also concluded in their study that establishing the diagnosis of ARMS in older adults is usually neglected due to its rarity in this age group, lack of a characteristic alveolar pattern, and CD 56 positivity.
To conclude, CD 56 positive cells should be cautiously studied, we should employ a panel of markers, including desmin, myogenin/MyoD1, and genetic study in the diagnosis of small round cell tumors so that the possibility of this condition is not overlooked.
Key message
We should employ a panel of markers including desmin and myogenin/MyoD1 in the diagnosis of small round cell tumors so that the possibility of this condition is not overlooked.
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Conflicts of interest
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References 
Correspondence Address:
Dr. Rani Sahu
C2A, Janakpuri Superspecialist Hospital, Delhi - 110 058
India
Source of Support: None, Conflict of Interest: None
CheckDOI: 10.4103/joc.joc_211_21
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