NDRG1 and neoplasm: The authors of this latter study chose those two cell lines because they are aggressive (namely migratory and are enriched in tumor-initiating cells), however, these reasons do not explain why NDRG1 knockdown did not reduce migration in MDA-MB-231 or SUM159 cells (both being aggressive, metastatic and enriched in tumor-initiating cells) in a different study 18.