Reduction of global 5-hydroxymethylcytosine is a poor prognostic factor in breast cancer patients, especially for an ER/PR-negative subtype

DNA methylation at the 5 position of cytosine (5mC) is an epigenetic hallmark in cancer. The 5mC can be converted to 5-hydroxymethylcytosine (5hmC) through a ten-eleven-translocation (TET). We investigated the impact of 5mC, 5hmC, TET1, and TET2 on tumorigenesis and prognosis of breast cancer. Immunohistochemistry was used to assess the levels of 5mC, 5hmC, TET1, and TET2 in the corresponding tumor adjacent normal (n = 309), ductal carcinoma in situ (DCIS, n = 120), and invasive ductal carcinoma (IDC, n = 309) tissues for 309 breast ductal carcinoma patients. 5mC, 5hmC, TET1-n, and TET2-n were significantly decreased during DCIS and IDC progression. In IDC, the decrease of 5hmC was correlated with the cytoplasmic mislocalization of TET1 (p < 0.001) as well as poor disease-specific survival (DSS) (adjusted hazard ratio [AHR] 1.95, p = 0.003) and disease-free survival (DFS) (AHR 1.91, p = 0.006). The combined decrease of 5mC and 5hmC was correlated with worse DSS (AHR 2.19, p = 0.008) and DFS (AHR 1.99, p = 0.036). Stratification analysis revealed that the low level of 5mC was associated with poor DSS (AHR 1.89, p = 0.044) and DFS (AHR 2.02, p = 0.035) for the ER/PR-positive subtype. Conversely, the low level of 5hmC was associated with worse DSS (AHR 2.77, p = 0.002) and DFS (AHR 2.69, p = 0.006) for the ER/PR-negative subtype. The decreases of 5mC, 5hmC, TET1-n, and TET2-n were biomarkers of tumor development. The global reduction of 5hmC was a poor prognostic factor for IDC, especially for ER/PR-negative subtype.