Given previous studies linking Ahr function with maintenance of the cancer-propagating cell (CPC) compartment36,37 and the evidence supporting a role for Sox2+ CPCs in promoting SHH medulloblastoma aggressiveness20,21, we decided to investigate whether the elevated SMAD3 activity in Ahr-deficient medulloblastoma modulated important CPC properties. The gene discussed is AHR; the disease is medulloblastoma.