Whole-exome sequencing of pancreatic neoplasms with acinar differentiation

Abstract

Pancreatic carcinomas with acinar differentiation, including acinar cell carcinoma, pancreatoblastoma and carcinomas with mixed differentiation, are distinct pancreatic neoplasms with poor prognosis. Although recent whole-exome sequencing analyses have defined the somatic mutations that characterize the other major neoplasms of the pancreas, the molecular alterations underlying pancreatic carcinomas with acinar differentiation remain largely unknown. In the current study, we sequenced the exomes of 23 surgically resected pancreatic carcinomas with acinar differentiation. These analyses revealed a relatively large number of genetic alterations at both the individual base pair and chromosomal levels. There was an average of 119 somatic mutations/carcinoma. When three outliers were excluded, there was an average of 64 somatic mutations/tumour (range 12-189). The mean fractional allelic loss (FAL) was 0.27 (range 0-0.89) and heterogeneity at the chromosome level was confirmed in selected cases using fluorescence in situ hybridization (FISH). No gene was mutated in >30% of the cancers. Genes altered in other neoplasms of the pancreas were occasionally targeted in carcinomas with acinar differentiation; SMAD4 was mutated in six tumours (26%), TP53 in three (13%), GNAS in two (9%), RNF43 in one (4%) and MEN1 in one (4%). Somatic mutations were identified in genes in which constitutional alterations are associated with familial pancreatic ductal adenocarcinoma, such as ATM, BRCA2 and PALB2 (one tumour each), as well as in genes altered in extra-pancreatic neoplasms, such as JAK1 in four tumours (17%), BRAF in three (13%), RB1 in three (13%), APC in two (9%), PTEN in two (9%), ARID1A in two (9%), MLL3 in two (9%) and BAP1 in one (4%). Perhaps most importantly, we found that more than one-third of these carcinomas have potentially targetable genetic alterations, including mutations in BRCA2, PALB2, ATM, BAP1, BRAF and JAK1.

Keywords: acinar cell carcinoma; carcinoma; genetics; pancreas; pancreatoblastoma; sequencing.