A Novel GLCCI1::BRAF Fusion With Independent MYC and MYCN Amplifications in Pediatric Pancreatic Acinar Cell Carcinoma.

Pediatric pancreatic acinar cell carcinoma (PACC) is a rare malignancy, comprising 5-15% of pediatric pancreatic tumors. BRAF rearrangement is found in 20%-30% of PACC cases. We report a case of PACC with a novel GLCCI1::BRAF fusion and independent amplifications in MYC and MYCN. A 10-year-old male presented with 6 months of weight loss, back pain, and loose stools. Imaging demonstrated concentric soft tissue thickening around the superior mesenteric artery, prompting biopsy of a periaortic lymph node showing metastatic PACC. Pancreaticoduodenectomy revealed PACC and metastatic deposits in multiple lymph nodes and retroperitoneal soft tissue. Fluorescence in situ hybridization of both the periaortic lymph node and pancreaticoduodenectomy specimens demonstrated BRAF gene rearrangement, with the partner identified as GLCCI1 by next generation sequencing and fusion assays. Chromosomal microarray analysis demonstrated amplification of MYC in the periaortic lymph node biopsy and amplification of MYCN in the resection specimen. The patient was treated with neoadjuvant chemotherapy, radiation, and a pan-RAF inhibitor, but developed new widespread metastasis and was deceased 22 months after presentation. The combination of the primary GLCCI1::BRAF fusion with secondary amplification of MYC and MYCN is likely to drive the aggressive behavior and metastasis in this case of PACC.