The correlation analysis showed that G9a mRNA level was inversely correlated with DKK1 (Additional file 2: Figure S4a, P = 0.00828, R = − 0.38) and WIF1 (Additional file 2: Figure S4b, P = 0.0403, R = − 0.3) in 46 of lung cancer tissues, and a slight reverse but insignificant correlation between APC2 and G9a was observed in lung cancer tissues (data not shown). Here, DKK1 is linked to lung cancer.