CEACAM5 and neoplasm: The role of mast cells in mediating TH9 cell-dependent anti-tumor immune responses was further investigated in an elegant study from Abdul-Wahid et al., who interrogated the cellular bases accounting for the anti-tumor efficacy of a vaccine containing the carcinoembryonic antigen (CEA) IgV-like N domain and the toll-like receptor 3 ligand poly I:C that elicited TH9 cell responses in vivo.