BRCA2 Male Breast Cancer and Pancreatic Cancer Risk

A 58-year-old man of Ashkenazi Jewish descent presents with a 1.5 cm subareolar left breast mass. Biopsy confirms invasive ductal carcinoma (ER+, PR+, HER2−). Family history is significant for his sister with breast cancer at 44, father with metastatic pancreatic adenocarcinoma at 62, and paternal uncle with high-Gleason prostate cancer at 55. Germline genetic testing identifies a pathogenic truncating mutation in the BRCA2 gene located at the locus marked **A** in the diagram. Which of the following best describes the molecular consequence of BRCA2 loss of function in this patient's tumor cells?