Expression of Myxovirus Resistance A (MxA) Is Associated with Tumor-Infiltrating Lymphocytes in Human Epidermal Growth Factor Receptor 2 (HER2)-Positive Breast Cancers

Purpose The prognostic significance of tumor-infiltrating lymphocytes (TILs) has been determined in breast cancers. lnterferons can affect T-cell activity through direct and indirect mechanisms. Myxovirus resistance A (MxA) is an excellent marker of interferon activity. Here, we evaluated TILs and MxA expression in human epidermal growth factor receptor 2 (HER2)-positive breast cancers. Materials and Methods Ninety cases of hormone receptor (HR)+/HER2+ tumors and 78 eases of HR-/HER2+ tumors were included. The TILs level was assessed using hematoxylin and eosin-stained full face sections, and MxA expression was evaluated by immunohistochemistry with a tissue microarray. Results MxA protein expression was significantly higher in tumors with high histologic grade (p=0.023) and high levels of TILs (p=0.002). High levels of TILs were correlated with high histological grade (p=0.001), negative lymphovascular invasion (p=0.007), negative lymph node metastasis (p=0.007), absence of HR expression (p < 0.001), abundant tertiary lymphoid structures (TLSs) around ductal carcinoma in situ (p=0.018), and abundant TLSs around the invasive component (p < 0.001). High levels of TILs were also associated with improved disease-free survival, particularly in HR-/HER2+ breast cancers. However, MxA was not a prognostic factor. Conclusion High expression of MxA in tumor cells was associated with high levels of TILs in HER2-positive breast cancers. Additionally, a high level of TILs was a prognostic factor for breast cancer, whereas the level of MxA expression had no prognostic value.