MYBL1-NFIB Fusions in Adenoid Cystic Carcinoma

Purpose: Adenoid cystic carcinoma (ACC) is an indolent salivary gland malignancy, characterized by t(6;9) translocations and MYB–NFIB gene fusions in approximately 50% of the tumors. The genetic alterations underlying t(6;9)-negative and t(6;9)-positive/MYB–NFIB fusion–negative ACC remain unknown. To uncover the genetic alterations in ACC lacking the canonical translocation and fusion transcript and identify new abnormalities in translocation positive tumors.

Experimental Design: We performed whole-genome sequencing in 21 salivary ACCs and conducted targeted molecular analyses in a validation set (81 patients). Microarray gene-expression data were also analyzed to explore the biologic differences between fusion positive and negative tumors.

Results: We identified a novel MYBL1–NFIB gene fusion as a result of t(8;9) translocation and multiple rearrangements in the MYBL1 gene in 35% of the t(6;9)-negative ACCs. All MYBL1 alterations involved deletion of the C-terminal negative regulatory domain and were associated with high MYBL1 expression. Reciprocal MYB and MYBL1 expression was consistently found in ACCs. In addition, 5'-NFIB fusions that did not involve MYB/MYBL1 genes were identified in a subset of t(6;9)-positive/fusion-negative tumors. We also delineated distinct gene-expression profiles in ACCs associated with the length of the MYB or MYBL1 fusions, suggesting a biologic importance of the C-terminal part of these fusions.

Conclusions: Our study defines new molecular subclasses of ACC characterized by MYBL1 rearrangements and 5'-NFIB gene fusions. Clin Cancer Res; 22(3); 725–33. ©2015 AACR.

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