During S phase, geminin is a negative regulator of DNA replication. In many cancer cell lines, inhibition of geminin by RNA interference results in re-replication of portions of the genome, which leads to aneuploidy. In these cell lines, geminin knockdown leads to markedly slowed growth and apoptosis within several days. However, the same is not true for primary and immortalized human cell lines, where other mechanisms exists to prevent DNA re-replication. Since geminin knockdown leads to cell death in many cancer cell lines but not primary cell lines, it has been proposed as a potential therapeutic target for cancer treatment.