TFRC and nonpapillary renal cell carcinoma: TfR1 elevation is a well-described feedback response to low cellular reactive iron (25, 26), and our previous finding of lower TfR1 expression in ccRCC and pRCC tumors relative to chRCC tumors (28) may reflect the higher iron content of ccRCC and pRCC tumors relative to chRCC tumors suggested by the current study.