CD44 and neoplasm: Moreover, given the low incidence of CD44+/CD24+ expression within ALDHhigh cell populations (0.48% of ALDHhigh cells), the presence of even one ALDHhigh/CD44+/CD24+ cell among 100 implanted ALDHhigh cells is quite unlikely and, further still, would not likely account for the 100% incidence of tumor formation we observed within this purified cell sub-population.