Alternative Lengthening of Telomeres and Loss of DAXX/ATRX Expression Predicts Metastatic Disease and Poor Survival in Patients with Pancreatic Neuroendocrine Tumors

Abstract

Purpose: Pancreatic neuroendocrine tumors (PanNET) are a heterogeneous group of neoplasms with increasing incidence and unpredictable behavior. Whole-exome sequencing has identified recurrent mutations in the genes DAXX and ATRX, which correlate with loss of protein expression and alternative lengthening of telomeres (ALT). Both ALT and DAXX/ATRX loss were initially reported to be associated with a favorable prognosis; however, recent studies suggest the contrary. Our aims were to assess the prevalence and prognostic significance of ALT and DAXX/ATRX in both primary and metastatic PanNETs.

Experimental design: Telomere-specific FISH and DAXX/ATRX IHC was performed on a multi-institutional cohort of 321 patients with resected PanNET and 191 distant metastases from 52 patients. These results were correlated with clinicopathologic features, including disease-free survival (DFS) and disease-specific survival (DSS).

Results: The prevalence of ALT and DAXX/ATRX loss in resected PanNETs was 31% and 26%, respectively, and associated with larger tumor size, higher WHO grade, lymph node metastasis, and distant metastasis (P < 0.001). The 5-year DFS and 10-year DSS of patients with ALT-positive and DAXX/ATRX-negative PanNETs were 40% and 50%, respectively, as compared with 96% and 89%, respectively, for wild-type PanNETs. Among distant metastases, ALT and DAXX/ATRX loss was 67% and 52%, respectively, and only occurred in the setting of an ALT-positive and DAXX/ATRX-negative primary PanNET. By multivariate analysis, both ALT and DAXX/ATRX loss were negative, independent prognostic factors for DFS.

Conclusions: ALT and DAXX/ATRX loss in PanNETs was associated with shorter DFS and DSS and likely plays a significant role in driving metastatic disease. Clin Cancer Res; 23(2); 600-9. ©2016 AACR.

Figure 1.

Representative examples of PanNETs assessed by DAXX and ATRX IHC and telomere-specific FISH. A, PanNET with preserved nuclear expression for both DAXX (B) and ATRX (C) and absence of the ALT phenotype (D). E, PanNET with DAXX loss (F), but preserved expression for ATRX (G). The loss of DAXX expression correlated with the presence of large, ultrabright intranuclear foci by telomere-specific FISH, consistent with ALT (H). I, PanNET with preserved expression for DAXX (J), but ATRX loss (K) and ALT positive (L) by telomere-specific FISH.

Figure 2.

Intratumoral heterogeneity for DAXX/ATRX protein expression and ALT in PanNETs. A, PanNET with preserved nuclear expression for DAXX (B), but ATRX loss (C, top right) within a subpopulation of neoplastic cells. Within areas of ATRX loss, telomere-specific FISH revealed large, bright signals consistent with ALT (D).

Figure 3.

Kaplan–Meier curves comparing the cumulative probabilities of DFS and DSS after surgical resection among PanNET patients with respect to ALT and DAXX/ATRX status. Patients with ALT-positive and DAXX/ATRX-negative PanNETs were associated with shorter DFS (A, B) and shorter DSS (C, D), as compared with patients with ALT-negative and DAXX/ATRX-positive PanNETs.