It showed that T‐synthase, the only enzyme that galactosylates the Tn antigen to form mature core 1‐derived O‐glycans [16], was also absent in Cosmc‐deficient cancer cells, which was in accordant with previous reports that Cosmc is a required molecular chaperone for active T‐synthase formation [17, 18]. Here, C1GALT1C1 is linked to cancer.