Chronic inflammation has been proposed to support the development of cancer.48, 49 In accordance with a previous study,50 our in vivo data show an increased inflammatory response in Rac1-EKO mice upon UV-irradiation as shown by increased numbers of γδ T cells and neutrophils in the skin of Rac1-EKO mice (Supplementary Figure S4). Here, RAC1 is linked to cancer.