Cytomorphologic, immunophenotypical and molecular features of pancreatic acinar cell carcinoma

Whole genome and transcriptome analysis of pancreatic acinar cell carcinoma elucidates mechanisms of homologous recombination deficiency and unravels novel relevant fusion events

Pancreatic acinar cell carcinoma (PACC) is a rare pancreatic tumor with a heterogeneous clinical course and, except for radical surgery, limited treatment options. We present a comprehensive study encompassing whole-genome and RNA sequencing of 7 tumor samples from 3 metastatic PACC patients to further delineate its genomic landscape and potential therapeutic implications. Our findings reveal distinct signatures of homologous recombination deficiency (HRD) in patients harboring pathogenic germline BRCA1/2 and FANCL mutations, demonstrating favorable responses to poly (ADP-ribose) polymerase 1 (PARP) inhibitors with prolonged disease-free intervals. Additionally, we first describe structural variants in PACC, including BRCA1::TRIM47 fusion and another variant impacting FANCC, both events related to HRD, and we also identify alterations in the mitogen-activated protein kinase (MAPK) pathway, including RAF1 duplication as well as novel BRAF::SORBS2 and MAP7D2::SND1 gene fusions, offering potential targets for therapy. Our study underscores the importance of genome and transcriptome-wide profiling of PACC, to help guide personalized treatment strategies to improve patient outcomes.

Risk of malignancy and overall survival associated with the diagnostic categories in the World Health Organization Reporting System for Pancreaticobiliary Cytopathology

BACKGROUND

The World Health Organization (WHO) classification system revised the Papanicolaou Society of Cytopathology (PSC) system for reporting pancreaticobiliary cytopathology. To better stratify intraductal and/or cystic neoplasms by cytologic grade, the neoplastic, other category was replaced by two new categories: pancreaticobiliary neoplasm, low-risk/grade (PaN-Low) and pancreaticobiliary neoplasm, high-risk/grade (PaN-High). Low-grade malignancies were placed in the malignant category, and benign neoplasms were placed in the benign/negative for malignancy category.

METHODS

An institutional pathology database search identified patients who underwent endoscopic ultrasound-guided fine-needle aspiration (EUS-FNA) for pancreatic lesions from January 2015 to April 2022. The absolute risk of malignancy (ROM) was determined by histologic and/or clinical follow-up of at least 6 months, and overall survival rates were calculated across diagnostic categories, comparing the WHO and PSC systems.

RESULTS

In total, 1012 cases were reviewed and recategorized. The ROM for the WHO system was 8.3% for insufficient/inadequate/nondiagnostic, 3.2% for benign/negative for malignancy, 24.6% for atypical, 9.1% for PaN-Low, 46.7% for PaN-High, 75% for suspicious for malignancy, and 100% for malignant. Comparatively, the ROM for the PSC system was 7.4% for nondiagnostic, 3.0% for negative for malignancy, 23.1% for atypical, 0% for neoplastic, benign, 7.3% for neoplastic, other, 75% for suspicious for malignancy, and 100% for malignant. The WHO system demonstrated superior stratification for overall survival.

CONCLUSIONS

The WHO system significantly improves the stratification of ROM and overall survival across diagnostic categories by introducing the PaN-Low and PaN-High categories and reassigning low-grade malignancies to the malignant category. Analyzing EUS-FNA samples with the WHO system provides critical insights for guiding clinical management.

Fusion genes in pancreatic tumors

Gene fusions and rearrangements play a crucial role in tumor biology. They are rare events typically detected in KRAS wild-type (WT) pancreatic tumors. Their identification can inform clinical management by enabling precision oncology, as fusions involving BRAF, FGFR2, RET, NTRK, NRG1, and ALK represent actionable targets in KRAS-WT cancers, and serve diagnostic purposes since fusions involving PRKACA/B represent the diagnostic hallmark of intraductal oncocytic papillary neoplasms (IOPNs). Although they are rare, the therapeutic and diagnostic importance of these genomic events should not be underestimated, highlighting the need for quality-ensured molecular diagnostics in the management of cancer. Herein we review the existing literature on the role of fusion genes in pancreatic tumors and their clinical potential as effective biomarkers and therapeutic targets.

Comprehensive review of pancreatic acinar cell carcinoma: epidemiology, diagnosis, molecular features and treatment

Pancreatic acinar cell carcinoma is a rare form (0.2-4.3%) of pancreatic neoplasm with unique clinical and molecular characteristics, which largely differ from pancreatic ductal adenocarcinoma. Pancreatic acinar cell carcinoma occurs more frequently in males and can occur in children. Serum lipase is elevated in 24-58% of patients with pancreatic acinar cell carcinoma. Pancreatic acinar cell carcinomas tend to be large at diagnosis (median tumour size: ~5 cm) and are frequently located in the pancreas head. Radiologically, pancreatic acinar cell carcinoma generally exhibits a solid appearance; however, necrosis, cystic changes and intratumoral haemorrhage can occur in larger lesions. Immunostaining is essential for the definitive diagnosis of pancreatic acinar cell carcinoma. Compared with pancreatic ductal adenocarcinoma, pancreatic acinar cell carcinoma has a more favourable prognosis. Although radical surgery is recommended for patients with pancreatic acinar cell carcinoma who do not have distant metastases, the recurrence rate is high. The effectiveness of adjuvant therapy for pancreatic acinar cell carcinoma is unclear. The response to FOLFIRINOX is generally favourable, and some patients achieve a complete response. Pancreatic acinar cell carcinoma has a different genomic profile compared with pancreatic ductal adenocarcinoma. Although genomic analyses have shown that pancreatic acinar cell carcinoma rarely has KRAS, TP53 and CDKN2A mutations, it has a higher prevalence of homologous recombination-related genes, including BRCA1/2 and ATM, than pancreatic ductal adenocarcinoma, suggesting high sensitivity to platinum-containing regimens and PARP inhibitors. Targeted therapies for genomic alternations are beneficial. Therefore, genetic testing is important for patients with pancreatic acinar cell carcinoma to choose the optimal therapeutic strategy.