IL4 and mycosis fungoides: Aberrant cytokine expression in the MF/SS tumor microenvironment (TME) is one of the most important factors in disease pathogenesis and progression [9,10]: while reactive T helper type 1 (Th1) and CD8+ tumor-infiltrating lymphocytes are found in the TME of early-stage MF/SS, disease progression is accompanied by infiltration with benign and malignant T lymphocytes producing mostly T helper type 2 (Th2) cytokines (IL-4, IL-5 and IL-13) [11].