In the skin, the major sources of IL-7 and IL-15 are fibroblasts and keratinocytes, and the upregulated production of IL-7 is reported in the hair follicles of both MF and SS [52,53], suggesting the role of IL-7 in the recruitment, survival, and proliferation of malignant T cells in CTCL lesions. Here, IL15 is linked to synovial sarcoma.