Pancreatic adenocarcinoma in a patient with a germline RB1 pathogenic variant

Germline pathogenic variants (GPVs) in RB1 are associated with the pediatric-onset intra-ocular malignancy retinoblastoma and typically present in infancy as multi-focal or bilateral disease. Survivors of retinoblastoma are at high risk for developing subsequent malignant neoplasms (SMNs); indeed, these are the leading cause of death for individuals cured of their retinoblastoma. With the exception of sarcomas, typically occurring at the site of antecedent radiation therapy for the original retinoblastoma diagnosis, and melanoma, little is known of other SMNs in retinoblastoma survivors. Here, we describe a unique case of pancreatic adenocarcinoma (PDAC) in a patient with a RB1 GPV who was diagnosed with retinoblastoma as an infant. At age 57, he was diagnosed with PDAC. Sequence analysis of the PDAC revealed the acquisition of a somatic second-hit in RB1 in the PDAC. Multispectral immunofluorescence analyses of the PDAC tumor illustrated selective loss of the RB protein in the tumor that was accompanied by the continued expression of p16^ink4a, encoded by the CDKN2A gene. In PDAC, CDKN2A loss is a common early event that contributes to carcinogenesis. This case may suggest that PDAC is a rare late component of RB1-associated tumor predisposition and illustrates that biallelic loss of RB1 is an alternative mechanism by which the RB1-pathway can be disrupted in PDAC independent of CDKN2A inactivation.