Q. A 61-year-old woman is admitted to the hospital for worsening symptoms of abdominal pain and vomiting over a 3-day period. Her records show a history of advanced cervical cancer previously treated with radiotherapy and chemotherapy. At admission, the patient’s blood pressure is 108/75 mm Hg supine, and 95/60 mm Hg standing. Her laboratory studies are shown below. Which of the following is the most likely cause of the patient’s acidic urine?