CD8A and breast carcinoma: Third, newly diagnosed HER2+ breast cancer patients with higher Il21r expression may have a reduced risk of distant relapse when treated with trastuzumab (anti-HER2/ErB2 mAb) in combination with chemotherapy; IL-21R expression on CD8+ effector T cells, not NK cells, is required for optimal anti-ErB2 mAb efficacy (29).