Fluorescence in-situ hybridization identifies Mastermind-like 2 (MAML2) rearrangement in odontogenic cysts with mucous prosoplasia: a pilot study

Aims The pathogenesis of intraosseous mucoepidermoid carcinoma (IMEC) remains unknown. Coexistence with odontogenic cysts (ODC) has been reported in 32–48% of IMEC. Furthermore, prosoplastic mucous cells are often seen in the epithelial lining of ODCs. MECT1–MAML2 fusion transcripts have been identified in >66% of salivary gland MEC cases. The aim of this study was to investigate the presence of MAML2 rearrangement in ODCs featuring mucous prosoplasia. Methods and results Ten cases of ODC with a mucous cell component and three cases of IMEC were evaluated using fluorescence in‐situ hybridization. All cases occurred in the mandible. The ODCs exhibited a M:F ratio of 4:1 (mean age 49.2 years), while all IMECs occurred in women (mean age 68.3 years). All three IMECs demonstrated MAML2 rearrangement, in 26–61% of tumour cells. Successful hybridization was observed in nine of 10 cases of ODC. In two of these nine, there was MAML2 rearrangement in 12% and 24% of the lining epithelial cells, while three of the nine showed rearrangement in 7–8% of cells; the remaining four cases were negative. Conclusions We identified MAML2 rearrangements in five of nine ODCs lined by mucus‐secreting cells. This suggests that at least a subset of ODCs with mucous prosoplasia are characterized by molecular events considered diagnostic for intraosseous and extraosseous MEC.