TKTL1 and cancer: Despite being considered a tumor suppressor because it halts cells in the G1 phase, CDH1 loss‐of‐function mutations have not been observed in cancers.[13] In contrast, CDH1 is frequently overexpressed in malignant tumors.[34] This paradox likely arises because R5P levels are low in proliferating cells, which prevents the TKTL1‐mediated degradation of CDH1.