Whole-exome sequencing of calcitonin-producing pancreatic neuroendocrine neoplasms indicates a unique molecular signature

Introduction

Calcitonin-producing pancreatic neuroendocrine neoplasms (CT-pNENs) are an extremely rare clinical entity, with approximately 60 cases reported worldwide. While CT-pNENs can mimic the clinical and diagnostic features of medullary thyroid carcinoma, their molecular profile is poorly understood.

Methods

Whole-exome sequencing (WES) was performed on tumor and corresponding serum samples of five patients with increased calcitonin serum levels and histologically validated calcitonin-positive CT-pNENs. cBioPortal analysis and DAVID gene enrichment analysis were performed to identify dysregulated candidate genes compared to control databases. Immunohistochemistry was used to detect the protein expression of MUC4 and MUC16 in CT-pNEN specimens.

Results

Mutated genes known in the literature in pNENs like MEN1 (35% of cases), ATRX (18-20% of cases) and PIK3CA (1.4% of cases) were identified in cases of CT-pNENs. New somatic SNVs in ATP4A, HES4, and CAV3 have not been described in CT- pNENs, yet. Pathogenic germline mutations in FGFR4 and DPYD were found in three of five cases. Mutations of CALCA (calcitonin) and the corresponding receptor CALCAR were found in all five tumor samples, but none of them resulted in protein sequelae or clinical relevance. All five tumor cases showed single nucleotide variations (SNVs) in MUC4, and four cases showed SNVs in MUC16, both of which were membrane-bound mucins. Immunohistochemistry showed protein expression of MUC4 in two cases and MUC16 in one case, and the liver metastasis of a third case was double positive for MUC4 and MUC16. The homologous recombination deficiency (HRD) score of all tumors was low.

Discussion

CT-pNENs have a unique molecular signature compared to other pNEN subtypes, specifically involving the FGFR4, DPYD, MUC4, MUC16 and the KRT family genes. However, a major limitation of our study was the relative small number of only five cases. Therefore, our WES data should be interpreted with caution and the mutation landscape in CT-pNENs needs to be verified by a larger number of patients. Further research is needed to explain differences in pathogenesis compared with other pNENs. In particular, multi-omics data such as RNASeq, methylation and whole genome sequencing could be informative.

Calcitonin-Producing Neuroendocrine Neoplasms of the Pancreas: Clinicopathological Study of 25 Cases and Review of the Literature

Increased levels of circulating calcitonin are a clue in the diagnosis of medullary thyroid carcinoma. However, hypercalcitoninemia can also be related to other pathological conditions, including pancreatic neuroendocrine neoplasms (PanNENs). Ectopic hormonal production is not unusual in both functioning and non-functioning PanNENs; however, little is known about the frequency of calcitonin expression in these neoplasms. The aims of this study were to assess the frequency of calcitonin immunoreactivity in PanNENs, independently from serum calcitonin levels, and to evaluate the clinicopathological and prognostic features of calcitonin-immunoreactive (Cal-IR) PanNENs, including a comparison with cases already reported in the literature. We screened 229 PanNENs for the immunohistochemical expression of calcitonin, including both functioning and non-functioning neoplasms, as well as both well-differentiated and poorly differentiated PanNENs. Both the clinicopathological data and the follow-up information were available and were compared with the immunohistochemical results. In addition, we reviewed the features of the calcitonin-producing PanNENs previously reported in the literature. Calcitonin was expressed in 25 of our 229 PanNENs (10.9%). Examples of well- and poorly differentiated, as well as both functioning and non-functioning PanNENs, were found to be calcitonin immunoreactive. Cal-IR PanNENs did not show any significant difference with the whole series of neoplasms included in the study, when the clinicopathological parameters were considered, except for a younger age at diagnosis and for a larger size of the tumor in non-functioning Cal-IR PanNENs. Taken together, our results show that calcitonin immunoreactivity is not an exceptional event in PanNENs. Furthermore, calcitonin expression does not identify a separate clinical entity, in contrast to other PanNENs with ectopic hormone production, such as adrenocorticotropic hormone (ACTH)-producing PanNENs, which show a distinctively more aggressive behavior.