HIF1A and nonpapillary renal cell carcinoma: Because one-third of ccRCC tumors with VHL loss-of-function exclusively overexpress HIF-2α (“H2”) and two-thirds overexpress both HIF-1α and HIF-2α (“H1H2”) [44], we analyzed two VHL mutant ccRCC cell lines, 786-O and RCC4, which represent the H2 and H1H2 subtypes, respectively.