title: Analysis of MAML2 rearrangement in mucoepidermoid carcinoma of the thymus.
abstract: Primary thymic mucoepidermoid carcinoma (TMEC) is rare. High-grade TMEC can be difficult to distinguish from poorly differentiated squamous cell carcinoma and adenosquamous carcinoma. A strong association between mucoepidermoid carcinoma (MEC) and t(11;19)(q21;p13) has been observed in other anatomical sites. Although this translocation is largely considered a disease-defining event for MEC, its incidence in TMEC has not been explored. In this study, we evaluate the value of identifying MAML2 rearrangement by fluorescence in situ hybridization (FISH) to distinguish TMEC from poorly differentiated squamous cell carcinoma and adenosquamous carcinoma. Cases of TMEC, moderate to poorly differentiated squamous cell carcinoma, and adenosquamous carcinoma were re-reviewed by 3 surgical pathologists and classified according to the current World Health Organization classification of thymic tumors (2004). Cases of TMEC were histologically graded using the Brandwein system. FISH was used to detect MAML2 rearrangements using a break-apart probe. FISH for MAML2 rearrangement was performed on cases of TMEC (n = 2), thymic squamous cell carcinoma (n = 5), and thymic adenosquamous carcinoma (n = 3). The 2 cases of TMEC showed MAML2 rearrangement. All other tested cases did not show rearrangement of MAML2. In conclusion, using FISH to identify MAML2 rearrangement is a valuable diagnostic tool in the evaluation of thymic malignancies, specifically, distinguishing TMEC from squamous cell carcinoma and adenosquamous carcinoma. These findings also suggest that TMEC has both histomorphologic and cytogenetic similarities to cases of MEC arising from other anatomical sites.
authors.affiliation: Department of Laboratory Medicine & Pathology, Mayo Clinic Rochester, Rochester 55905, MN, USA. Electronic address: Roden.anja@mayo.edu.
authors.forename: Anja C
authors.initials: AC
authors.lastname: Roden
authors.forename: Michele R
authors.initials: MR
authors.lastname: Erickson-Johnson
authors.forename: Eunhee S
authors.initials: ES
authors.lastname: Yi
authors.forename: Joaquín J
authors.initials: JJ
authors.lastname: García
mesh_terms: D000328:Adult; D000368:Aged; D018196:Carcinoma, Adenosquamous / Q000175:diagnosis* / Q000235:genetics / Q000473:pathology; D018277:Carcinoma, Mucoepidermoid / Q000175:diagnosis* / Q000235:genetics / Q000473:pathology; D002294:Carcinoma, Squamous Cell / Q000175:diagnosis* / Q000235:genetics / Q000473:pathology; D004268:DNA-Binding Proteins / Q000235:genetics*; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D008297:Male; D009687:Nuclear Proteins / Q000235:genetics*; D013953:Thymus Neoplasms / Q000175:diagnosis* / Q000235:genetics / Q000473:pathology; D015534:Trans-Activators; D014157:Transcription Factors / Q000235:genetics*; D014178:Translocation, Genetic
chemical_list: D004268:DNA-Binding Proteins; C471297:MAML2 protein, human; D009687:Nuclear Proteins; D015534:Trans-Activators; D014157:Transcription Factors
keywords: Fluorescence in situ hybridization; MAML2; Mucoepidermoid carcinoma; Thymic carcinoma