Cancer epigenetics: When TUG1 turns into a thug through excessive repression. Cyclin-dependent protein kinase inhibitors (CDKNs) keep the cell cycle in check to avoid uncontrolled cell growth. TUG1 lncRNA is overexpressed in gastric cancer wherein it binds PRC2. The pair binds to and trimethylates H3K27 at the p15, p16, p21, p27 and p57 CDKN gene loci, leading to their repression and to sustained cell growth. Knockdown of TUG1 reduces EZH2 binding to, and H3K27 trimethylation of all CDKN genes, with a concomitant derepression of all tested CDKNs, along with the inhibition of gastric tumor xenograft growth in mice. High TUG1 expression correlates to worse TNM stage and to metastasis in a cohort of 100 gastric cancer patients. Less than 40% of patients with high TUG1 expression versus more than 75% of patients with low TUG1 expression survive 36 months (Xu, Yin, De and coll., Nanjing Medical University, Jiangsu, China).