DDAH1 and nasopharyngeal carcinoma: Even cells derived from the same parental generation will gradually develop cellular heterogeneity during the passage process, there might be differences in gene expression among different individual cells, and such differences may become more pronounced after multiple passages, leading to changes in the protein expression of the overall cell population.[34] To investigate the cisplatin resistance mechanism in NPC cells, we focused on the relationship between DDAH1 and EGFR.