FasL expression in solid tumors is heterogenous, and high expression may simultaneously support metastatic spread17 and immune evasion.18 Fas-4-1BB IFP+ T cells preferentially accumulated relative to IFP- T cells even in E9 ID8VEGFFasL-/- tumors, indicating that FasL expression by tumor epithelium is not required for the improved persistence of IFP+ T cells in situ. The gene discussed is FASLG; the disease is neoplasm.