PROM1 and neoplasm: To determine which cell populations possessed the highest tumor-initiating potential, we injected purified ALDHhigh /CD133+, ALDHhigh /CD133−, ALDHlow/CD133+ and ALDHlow/CD133− cells from pooled F2 generation tumors derived from MDA-PATX5 into the subcutaneous flank of NOD/SCID mice in limiting dilutions (100, 500, and 1000 cells), as described in Materials and Methods.