Consultants:
Jason Phillips, MD, University of Colorado
Steven C. Campbell, MD PhD, Cleveland Clinic

A healthy 57‐year‐old man had a R radical nephrectomy at an outside hospital eight years previously. The pathology was pT2 (8 cm), clear cell RCC, grade 3, with negative margins. At four years follow‐up the CT scan showed no evidence of disease. Now the patient presents with dull R flank pain. Two representative images from the CT scan are shown:

Additional images confirm that this 6.9cm mass lies within the renal fossa and is juxtaposed against the IVC and liver with no clear fat planes identified between the mass and these structures.

What is the differential diagnosis?

What is the most likely diagnosis?