A 58-year-old man with a 40 pack-year smoking history undergoes contrast-enhanced CT abdomen for incidental flank pain. Imaging reveals a 6 cm left renal mass with heterogeneous enhancement and a thick irregular wall, as marked **A** in the diagram. The mass shows an increase in Hounsfield units of 28 after contrast administration. Which of the following is the most appropriate next management step for this patient?