Because trastuzumab can enhance CD4 + Th1 cell-regulated anti-tumor immune responses [16, 58], we investigated whether activated CD4 + Th1 cells could produce and secrete miR-19a-3p, thereby contributing to the increased levels of miR-19a-3p in the serum of patients with metastatic HER2 + breast cancer and a favorable prognosis. Here, ERBB2 is linked to breast cancer.