To determine which factors released by TSLP-stimulated Th2 cells are responsible for breast cancer suppression, we studied mutant CD4+ T cells that lacked either cytokines commonly associated with antitumor immunity (TNFα and IFNγ) or those that were highly expressed by TSLP-stimulated CD4+ Th2 cells (IL-3, IL-5, and GM-CSF). This evidence concerns the gene IL3 and breast carcinoma.