Glucagon-Producing Pancreatic Neuroendocrine Tumors (Glucagonomas) are Enriched in Aggressive Neoplasms with ARX and PDX1 Co-expression, DAXX/ATRX Mutations, and ALT (Alternative Lengthening of Telomeres)

Abstract

Glucagonomas are functioning pancreatic neuroendocrine tumors (PanNETs) responsible for glucagonoma syndrome. This study aims to shed light on the clinicopathological and molecular features of these neoplasms. Six patients with glucagonomas were identified. All neoplasms were investigated with immunohistochemistry for neuroendocrine markers (Synaptophysin, Chromogranin-A), ATRX, DAXX, ARX, and PDX1 transcription factors. Fluorescent in situ hybridization (FISH) for assessing alternative lengthening of telomeres (ALT), and next-generation sequencing (NGS) for molecular profiling were performed. All cases were large single masses (mean size of 8.2 cm), with necrolytic migratory erythema as the most common symptom (6/6 cases, 100%). All neoplasms were well-differentiated G1 tumors, except one case that was G2. The tumors consistently showed classic/conventional histomorphology, with solid-trabecular and nested architecture. Lymphatic and vascular invasion (6/6, 100%), perineural infiltration (4/6, 66.6%), and nodal metastasis (4/6, 66.6%) were frequently observed. Transcription factors expression showed strong ARX expression in all tumors, and PDX1 expression in 5/6 cases (83.3%), indicating co-occurring alpha- and beta-cell differentiation. NGS showed recurrent somatic MEN1 and ATRX/DAXX biallelic inactivation. Cases with ATRX or DAXX mutations also showed matched loss of ATRX or DAXX protein expression and ALT. One case harbored somatic MUTYH inactivation and showed a high tumor mutational burden (TMB, 41.0 mut/Mb). During follow-up, one patient died of the disease, and four patients developed distant metastasis. Pancreatic glucagonomas are distinct PanNETs with specific clinicopathological and molecular features, including histological aspects of biological aggressiveness, co-occurring alpha- and beta-cell differentiation, MEN1 and DAXX/ATRX mutations enrichment, and the possible presence of high-TMB as an actionable marker.

Keywords: ALT; ATRX; DAXX; Functioning; Glucagon; MUTYH; NET; Neuroendocrine.

Fig. 1

Highly representative microscopic images, stained with hematoxylin–eosin, of the histomorphology of the cases in the current series. All tumors show hypercellular areas with classic/conventional architecture and solid-trabecular features (A, B; A: 20 × original magnification, B: 20 ×). Areas of hyalinized fibrosis were also detected, representing up to 30% of the tumor mass (C, D; C:10 × , D: 20 ×). In one case (case #2), dystrophic calcifications were also present (black arrow in C). Nodal metastases were common and detected in 4 cases (E, 4 ×)

Fig. 2

Highly-representative images of some of the most relevant immunohistochemical analyses in the current series (original magnification 20 ×). After showing a classic example of tumor morphology (A, hematoxylin–eosin), we showed representative images of the following markers along with their expression pattern: ATRX (loss of expression, B), ARX (strong expression, C), PDX1 (intermediate expression, D), glucagon (strong expression, E), and somatostatin (negative, F)