A 3-year-old girl presents to the pediatric outpatient clinic with her mother, who noticed a firm, non-tender abdominal mass while bathing the child 2 weeks ago. The child is asymptomatic, with no fever, vomiting, or weight loss. Vital signs are normal. On examination, a 5 cm fixed mass is palpable in the left flank, crossing the midline. Hemoglobin is 10.2 g/dL (mild anemia), and urinalysis is normal. Abdominal ultrasound shows a heterogeneous left renal mass with areas of necrosis. Which of the following is the most appropriate next step in management?