A 38-year-old woman presents to the oncology clinic with a 2-year history of recurrent breast cancers—first a left-sided invasive ductal carcinoma diagnosed at age 36, now a right-sided lesion at age 38. Family history reveals her mother died of ovarian cancer at age 42, and her maternal grandmother had breast cancer at age 45. Genetic testing confirms a heterozygous frameshift mutation in exon 11 of the BRCA1 gene. Immunohistochemistry on her current tumor shows loss of p53 expression. Which of the following best explains the aggressive behavior and bilateral presentation in this patient?