ID2 and neoplasm: To assess whether Id2 and/or Aldh3a1 play a role in promoting the growth of tumour cells in the brain, 4T1-Luc cells were transduced with lentiviruses containing non-targeting control shRNA (shNTC) or shRNAs targeting Id2 (shId2) or Aldh3a1 (shAldh3a1) (Fig. 2a) and inoculated intracranially into BALB/c mice.