Performance of DAXX Immunohistochemistry as a Screen for DAXX Mutations in Pancreatic Neuroendocrine Tumors

The sensitivity and specificity of IHC for DAXX mutation are 85% and 95%, respectively. Last exon DAXX mutant PanNETs often show alternative lengthening of telomeres despite retained DAXX expression, likely due to escape of nonmediated decay.

All pancreatic neuroendocrine tumors (PanNETs) with DAXX mutations detected by sequencing and a subset of DAXX wild-type PanNETs were analyzed for DAXX expression by IHC.

Of 154 PanNETs with MSK-IMPACT testing, 36 (30%) harbored DAXX mutations. DAXX mutations were associated with TSC2 mutations (46% vs 10%, P < 0.0001), tended to co-occur with MEN1 mutations (63% vs 49%, P = 0.11), and tended to be mutually exclusive with ATRX mutations (11% vs 25%, P = 0.053). Of 27 available DAXX mutant PanNETs, 23 lost DAXX expression (85.2%). All 4 DAXX mutants with retained expression harbored DAXX mutations within the SUMO-interacting motif of the last exon. Telomere-specific fluorescence in situ hybridization demonstrated alternative lengthening of telomeres in all 4 cases. Of 20 PanNETs with wild-type DAXX, 19 retained DAXX IHC expression (95%). Conclusions: The sensitivity and specificity of IHC for DAXX mutation are 85% and 95%, respectively. Last exon DAXX mutant PanNETs often show alternative lengthening of telomeres despite retained DAXX expression, likely due to escape of nonmediated decay.