OFP-08-009 CRTC1/MAML2 fusion transcript in central mucoepidermoid carcinoma of mandible: Diagnostic/ Histogenetic implications D. Bell * * MD Anderson Cancer Center, Dept. of Pathology, Houston, TX, USA Objective: MEC typically arises from major/minor salivary glands. Intraosseous salivary carcinomas are extremely rare (2-3 % of all MECs reported). The t(11; 19) and its CRTC1/ MAML1 fusion transcript have been identified in MEC at different sites and are associated with development of a subset of these tumors. We report 9 examples of central MEC of the mandible, including a case with a history of primary retromolar MEC. Method: RT-PCR and DNA sequencing analyses used to study microdissected components of 9 central MEC and 1 noncentral MEC. Of the central MEC tumors, 5 arose from ectopic salivary rests; others appeared to be of glandular odontogenic origins. Results: We identified CRTC1/MAML1 in 5 central MEC arising from ectopic salivary rests. This fusion transcript was not detected in non-central MEC or in another 4 central MEC arising from a glandular odontogenic etiology. Conclusion: Central MEC can manifest the fusion transcript in a subset of central MEC originating from ectopic salivary rests, and may have diagnostic/histogenetic roles in the future analysis of this entity, given the absence of the fusion transcript in MEC with glandular odontogenic precursors. Since the initial clinical and radiological diagnosis in three central low-grade MECs was a benign odontogenic cyst, our findings support a future role for the fusion analysis in initial diagnostic efforts.