CTNNB1 exon 3 mutations in metastatic solid pseudopapillary neoplasm of the pancreas

Solid pseudopapillary neoplasm (SPN) of the pancreas demonstrates an indolent disease course; however, some patients present with a "malignant" phenotype, including distant metastases resistant to chemotherapy. This analysis identifies molecular drivers of metastatic SPN using the world's largest clinicogenomics database.

The American Association for Cancer Research Project Genomics Evidence Neoplasia Information Exchange was queried for primary and metastatic SPN samples. Sample-level genomic alterations were compared. A pan-pancreatic cancer analysis assessed relevant mutations among all metastatic pancreatic malignancies.

Among 28 SPN samples identified (n = 17 primary, n = 11 metastatic), the most commonly mutated gene was CTNNB1, (24/28 samples; 85.7%). Most mutations were missense (21/24; 87.5%) or in-frame deletions (3/24; 12.5%). The most common CTNNB1 mutations in primary SPN were exon 3 S37F/C missense mutations (6/16 profiled patients, 37.5%), contrasting exon 3 D32N/Y/H missense mutations in metastatic samples (6/11 profiled patients, 54.5%). Metastatic SPN had higher rates of CTNNB1 mutations than metastases from pancreatic ductal adenocarcinoma (72.7% vs. 1.1%; q < 0.0001), pancreatic neuroendocrine tumor (72.7% vs. 2.5%; q < 0.0001), and pancreatic acinar cell carcinoma (72.7% vs. 11.5%; q = 0.0254).

Missense mutations along exon 3 of CTNNB1 predominate metastatic SPN, differentiating these patients from those with metastases from analogous pancreatic malignancies.