In this study, we show that previously identified MF-related features, such as expression of TOX and GATA3, are further enhanced in tissue as the patient progress and that the progression-associated clonotype specifically up-regulates transforming growth factor β1 (TGF-β1) prior to progression, which may be of interest to further investigate for future targeted treatment in sub-groups of MF patients. Here, TOX is linked to mycosis fungoides.