XRCC1 and lung carcinoma: In one study, researchers examined 3-methylcholanthrene (3-MCA)-induced lung cancer in a rat model and human lung cancer tissue samples and found that TET1 methylation levels were significantly upregulated while DNA hydroxymethylation levels in the promoter regions of XRCC1, OGG1, and APEX1, which are key genes of the BER pathway, were significantly reduced.