A 41-year-old woman presents with chest pain and dysphagia. Routine laboratory studies reveal profound neutropenia. The patient has a history of hepatitis B, hepatitis C, schizophrenia, and recent keratoplasty. Hemoglobin level is 12.3 g/dL; platelet count is normal. She smokes tobacco (4 or 5 cigarettes a day) and crack cocaine (2 or 3 times a week).