PROM1 and renal cell carcinoma: Unsorted RCC-41-PDX-2 produced spheroids in about 100% of the wells at 102 cells per well, while at the limiting dilution of 1 cell per well, RCC-41-PDX-2, sorted RCC-41-PDX-2/CD133− and RCC-41-PDX-2/CD133+ formed spheroids with respective efficiencies of 6, 3, and 1% (Figure 3B and 3C).