SLC44A4 and gastric cancer: PLOD2 catalyses the hydroxylation of lysyl residues and could promote the metastasis capacity of gastric cancer, sarcoma and colorectal cancer34–36 However, SLC44A4, which was reported to be upregulated in prostate and pancreatic cancers,37 was downregulated in malignant cells and correlated with a good prognosis for HNSCC, indicating an undefined role in tumor suppression that needs further elucidation.