Model to explain the clinical progression of mycosis fungoides. The MF clone produces a range of cytokines, predominantly IL-4 and IL-17, and initiates an immune response from TILs, even in early-stage disease. TILs develop an exhausted phenotype due to chronic engagement with tumor but continue to produce IFN-γ and IL-17. Disease progression occurs when the tumor evolves to attain 1 of 3 phenotypes that allow it to proliferate, despite continuing immune recognition from TILs. This state is associated with markedly reduced production of IL-17 by tumor and TIL populations.