IL1A and Familial prostate cancer: 1,25(OH)2D also induces cell cycle arrest and senescence in an IL‐1α‐dependent manner in prostate progenitor epithelial/stem cells isolated from adult mice in vitro.21 In vivo, dietary vitamin D or calcitriol supplementation reduced prostate cancer xenograft growth and increased 1,25(OH)2D serum levels.22 In another study, disruption of CYP24A1 activity increased 1,25(OH)2D levels and reduced prostate cancer growth in vitro and in vivo.23 However, the mechanism of action of 1,25(OH)2D was not defined well in these studies.