title: Nasopharyngeal alveolar rhabdomyosarcoma expressing CD56: a mimicker of extranodal natural killer/T-cell lymphoma.
abstract: Alveolar rhabdomyosarcoma (ARMS) is remarkably rare in adults older than 45 years. Histologically, the tumor is composed of blue round cells with frequent expression of CD56 in addition to myogenic markers. Recent studies of ARMS have shown two specific recurrent translocations: PAX3-FKHR [t(2;13)(q35;q14)] or PAX7-FKHR [t(1;13)(p36;q14)]. Extranodal natural killer (NK)/T-cell lymphoma (ENKTL) occurs most frequently in the upper aerodigestive tract with a male preference in East Asia and Central and South Americas with neoplastic cells frequently expressing CD56. We report a 53-year-old Taiwanese man presenting with a nasopharyngeal mass, cervical lymphadenopathy, and multiple bone metastases. Histologically, the nasopharyngeal biopsy revealed diffuse sheets of small blue round tumor cells without obvious alveolar pattern, angioinvasion or tumor necrosis. An initial erroneous diagnosis of ENKTL was made due to CD56 expression using fresh tumor tissue with flow cytometric analysis and the patient was treated accordingly. Retrospective study showed that the tumor cells expressed CD56, desmin, and myogenin. Fluorescence in situ hybridization revealed that the tumor cells were positive for FKHR gene rearrangement, confirming the diagnosis of ARMS. Our case illustrates that a diagnosis of ENKTL based solely on CD56 expression can be misleading for a nasopharyngeal small blue round cell tumor. ARMS should be included as a differential diagnosis, and a correct diagnosis can be reached only after a high index of suspicion and a thorough histological examination with the aid of ancillary studies.
authors.affiliation: Department of Pathology, Chi-Mei Medical Center Tainan, Taiwan ; Department of Pathology and Laboratory Medicine, Koo Foundation Sun Yat-Sen Cancer Center Taipei, Taiwan.
authors.forename: Khin Than
authors.initials: KT
authors.lastname: Win
authors.affiliation: Department of Pathology and Laboratory Medicine, Koo Foundation Sun Yat-Sen Cancer Center Taipei, Taiwan.
authors.forename: Ming-Yuan
authors.initials: MY
authors.lastname: Lee
authors.affiliation: Division of Hematology and Medical Oncology, Department of Medicine, Koo Foundation Sun Yat-Sen Cancer Center Taipei, Taiwan.
authors.forename: Tran-Der
authors.initials: TD
authors.lastname: Tan
authors.affiliation: Department of Pathology and Laboratory Medicine, Koo Foundation Sun Yat-Sen Cancer Center Taipei, Taiwan.
authors.forename: Mung-pei
authors.initials: MP
authors.lastname: Tsai
authors.affiliation: Department of Pathology, St. Jude Children's Research Hospital USA.
authors.forename: Armita
authors.initials: A
authors.lastname: Bahrami
authors.affiliation: Department of Pathology, St. Jude Children's Research Hospital USA.
authors.forename: Susana C
authors.initials: SC
authors.lastname: Raimondi
authors.affiliation: Department of Pathology, Chi-Mei Medical Center Tainan, Taiwan ; Department of Pathology, Taipei Medical University Taipei, Taiwan ; Department of Pathology, National Taiwan University Taipei, Taiwan.
authors.forename: Shih-Sung
authors.initials: SS
authors.lastname: Chuang
mesh_terms: D001706:Biopsy; D019002:CD56 Antigen / Q000096:biosynthesis*; D003951:Diagnostic Errors; D005434:Flow Cytometry; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors / Q000235:genetics; D006801:Humans; D007150:Immunohistochemistry; D016130:Immunophenotyping; D017404:In Situ Hybridization, Fluorescence; D054391:Lymphoma, Extranodal NK-T-Cell / Q000175:diagnosis*; D008297:Male; D008875:Middle Aged; D009303:Nasopharyngeal Neoplasms / Q000175:diagnosis* / Q000235:genetics; D018232:Rhabdomyosarcoma, Alveolar / Q000175:diagnosis* / Q000235:genetics
chemical_list: D019002:CD56 Antigen; C085126:FOXO1 protein, human; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; C522918:NCAM1 protein, human
keywords: Alveolar rhabdomyosarcoma; CD56; extranodal natural killer/T-cell lymphoma; flow cytometry; rhabdomyosarcoma