CD8A and thyroid cancer: To address this issue, studies have identified the increased immune suppressor cells, regulatory T cells (Tregs) (15), PD1+ T cells (15), myeloid-derived suppressor cells (MDSCs) (16), in circulation, and infiltrating the tumor of pathologically aggressive differentiated thyroid cancer (5, 17–19), while the association with effector CD8+ T cells has been mixed (20, 21).