Q. A 50-year-old woman presents to the clinic with complaints of lower back pain and fatigue. She reports that the symptoms have been present for several months, and have been gradually getting worse. She has a history of recurrent urinary tract infections. On physical examination, she has mild left-sided costovertebral angle tenderness. Laboratory studies show mild anemia and a creatinine level of 1.8 mg/dL. A non-contrast CT scan of the abdomen and pelvis shows asymmetric thickening of the left renal parenchyma with blunted calyces, and a small renal cyst. What is the most likely diagnosis?