Project Summary/Abstract Adenoid Cystic Carcinoma (ACC) is the second most common type of salivary gland tumor, but can also arise in other tissues such as lacrimal gland, breast and skin. ACC tumors display heterogeneous morphology and have a variable clinical course. Many ACC patients survive 10 years or more after the standard therapy of surgery and radiation, but a fraction succumb much more quickly and others acquire distant metastases or relapse 5 or more years after the initial treatment. So patients often have to endure significant morbidity including reconstructive surgery while living under the threat of recurrence for decades. ACC is one of the only human tumors in which mutations involving the MYB oncogene are known to be the most common driver. A large fraction of ACC tumors harbor a t(6;9) translocation, which juxtaposes an enhancer from the NFIB gene on chromosome 9p close to the MYB oncogene on chromosome 6q. However, ACC tumors have heterogeneous molecular characteristics. About half the tumors that express MYB harbor translocations that fuse the MYB and NFIB genes, resulting in a ‘broken’ or truncated MYB gene that can only express Myb proteins with C-terminal truncations – mutations that are known to activate the oncogenic potential of the Myb transcription factor. But the remaining MYB positive tumors appear to express full-length Myb proteins without any fusion to NFIB. And some tumors harbor different translocations that position the MYB gene close to other enhancers or that involve the related MYBL1 gene instead of MYB. This molecular heterogeneity is also reflected in the subgroups of ACC patients that have been identified by gene expression profiling, including at least one poor-prognosis subgroup with a unique gene expression profile and another subgroup that expresses neither MYB nor MYBL1 and must harbor as yet unidentified driver mutations. Deciphering the molecular events that lead to ACC has been complicated by the lack of adequate cell models for this tumor. To avoid any issues from highly selected or mislabeled cell lines, our strategy has been to utilize primary salivary gland ACC patient samples, an approach that has led to numerous important results that have reshaped our understanding of ACC tumors. In this competing renewal application we will generate the largest set of ACC tumor RNA-seq data in order to move the field forward in several ways. We will address the heterogeneity of ACC tumors and patients, set the stage for the development of new therapeutic strategies that target Myb proteins, use patient samples in a translational way to validate experimental results about Myb protein biology and we will begin migrating our approaches to clinical (CLIA) laboratories to make them usable in the clinic.