NARF and neoplasm: When only 1000 cells were injected (such that BCSCs were limiting), tumors formed in 10/10 mice injected with NTC cells, but only 3/10 and 2/9 mice injected with either of 2 NARF-knockdown subclones, indicating that NARF plays a critical role in BCSC specification and tumor initiation, as described above for PLXNB3.