PLE-5694

A 60-year-old male presents with gross hematuria. Upon further questioning, he reports a 3-month history of right-sided flank discomfort and abdominal fullness. His vital signs are as follows: BP: 170/100, HR: 122, RR: 22, T: afeb. During the physical examination, a right-sided lower abdominal mass is palpated. An abdominal CT scan is ordered, and the findings are consistent with renal cell carcinoma. Renal cell carcinoma is most commonly derived from cells of the: