Genetic profile of adenoid cystic carcinomas (ACC) with high-grade transformation versus solid type

Background: ACC can occasionally undergo dedifferentiation also referred to as high-grade transformation (ACCHGT).
However, ACC-HGT can also undergo transformation to adenocarcinomas which are not poorly differentiated. ACC-HGTis generally considered to be an aggressive variant of ACC, even more than solid ACC. This study was aimed to describe thegenetic changes of ACC-HGT in relation to clinico-pathological features and to compare results to solid ACC.
Methods: Genome-wide DNA copy number changes were analyzed by microarray CGH in ACC-HGT, 4 with transformationinto moderately differentiated adenocarcinoma (MDA) and two into poorly differentiated carcinoma (PDC), 5 solid ACC. Inaddition, Ki-67 index and p53 immunopositivity was assessed.
Results: ACC-HGT carried fewer copy number changes compared to solid ACC. Two ACC-HGT cases harboured a breakpointat 6q23, near the cMYB oncogene. The complexity of the genomic profile concurred with the clinical course of the patient.
Among the ACC-HGT, p53 positivity significantly increased from the conventional to the transformed (both MDA and PDC)component.
Conclusion: ACC-HGT may not necessarily reflect a more advanced stage of tumor progression, but rather a transformation toanother histological form in which the poorly differentiated forms (PDC) presents a genetic complexity similar to the solid ACC.