IL17A and neoplasm: Although cell surface markers provide a way to identify Th17 cells from other subsets, the recent finding that Th17 cells can convert into the Th1 lineage (gain an ability to secrete IFN-γ and lose their capacity to secrete IL-17) – a phenomenon referred to as “plasticity” (36) – has complicated our ability to discriminate these cells in the tumor-bearing host.