Review Question - QID 109677

A 59-year-old African American woman presents to the emergency department for fever and back pain that has persisted for 2 days. The patient states that the pain is episodic and intense. Her symptoms have not responded to acetaminophen. The patient endorses having lost 7 pounds recently without trying to lose weight. She also states that she has had abdominal pain and trouble focusing at work as well as a recent cough and fever which she attributes to allergies. The patient’s past medical history is notable for a recent distal radius fracture and a 50-pack-year smoking history. Her temperature is 99.5°F (37.5°C), blood pressure is 127/67 mmHg, pulse is 99/min, respirations are 14/min, and oxygen saturation is 98% on room air. Physical exam is notable for left-sided flank tenderness. The patient assumes an antalgic position in the stretcher. Chest radiography is performed as seen in Figure A. Laboratory studies are ordered as seen below.

Hemoglobin: 14 g/dL
Hematocrit: 44%
Leukocyte count: 10,500/mm^3 with normal differential
Platelet count: 195,000/mm^3

Serum:
Na+: 139 mEq/L
Cl-: 100 mEq/L
K+: 4.3 mEq/L
HCO3-: 25 mEq/L
BUN: 20 mg/dL
Phosphate: 1.5 mg/dL
Glucose: 99 mg/dL
Creatinine: 1.1 mg/dL
Ca2+: 12.2 mg/dL
AST: 12 U/L
ALT: 10 U/L

Ultrasound reveals unilateral hydronephrosis. Which of the following is the most likely underlying diagnosis for this patient’s presentation?