Review Question - QID 107982

A 45-year-old female presents to her primary care physician with a chief complaint of easy bruising and bleeding over the last 6 months. She has also noticed that she has been having fatty, foul smelling stools. Past history is significant for cholecystectomy a year ago to treat a long history of symptomatic gallstones. Based on clinical suspicion a coagulation panel was obtained showing a prothrombin time (PT) of 18 seconds (normal range 9-11 seconds), a partial thromboplastin time (PTT) of 45 seconds (normal 20-35 seconds), with a normal ristocetin cofactor assay (modern equivalent of bleeding time). Which of the following is the most likely cause of this patient's bleeding?