Differential association of 5-hydroxymethylcytosine levels with clinical and histopathological characteristics in breast cancer tumors.

Abstract

e23173 Background: Breast cancer is one of the top causes of cancer death worldwide. In Mexico, locally advanced breast cancer (LABC) comprises the majority of the breast cancer stages at diagnosis. Recent studies have suggested that 5-hydroxymethylcytosine (5hmC), could be a prognostic marker in breast cancer. However, the role of 5hmC on clinical and histopathologic characteristics in LABC has not been explored. Methods: From a cohort of locally advanced and advanced breast cancer patients treated at the National Cancer Institute in Mexico City with a 3-year follow-up, we measured 5hmC levels by immunodetection from fresh frozen tissue samples taken from the initial biopsy (N = 193). We determined the association between 5hmC levels and the most relevant clinical and histopathological characteristics. Results: From the full cohort analyzed; 42% were luminal A (n = 82), 33% were luminal B (N = 63), 9% were HER2-positive (N = 18), and 15% were triple-negative tumors. We found higher levels of global 5hmC in HER2 positive tumors vs. all other subtypes (p = 0.028, Kruskal-Wallis test). In luminal B tumors, 5hmC levels were associated with Ki67 (β = -0.04, 95%CI: -0.08, -0.01, p = 0.01 from multivariable model) but not in luminal A. Furthermore, we found that low 5hmC levels were associated with higher histological grade in HER2-positive tumors (p = 0.03, Kruskal-Wallis test). In subgroup analysis of LABC patients, we found higher 5hmC levels in non-ductal vs. ductal invasive tumors (β = 1.38, 95%CI: 0.049, 2.911, p = 0.043 from multivariable model). Also, lower 5hmC levels were associated with Ki67 (β = -2.53, 95%CI: -4.32, -0.74; p = 0.009 from multivariable model) and with histological type (p = 0.028, Kruskal-Wallis test) in LABC luminal B tumors. A borderline association with OS (p = 0.07, log-rank test) and RFS (p = 0.071, log-rank test) was observed in luminal A tumors in the LABC group. Conclusions: Our findings suggest that 5hmC levels are differentially associated with distinct clinical and histopathological characteristics in breast cancer, especially those linked to aggressiveness, including Ki67, histological type, and grade.