To determine whether Th2 polarization was required in CD4+ T cell immunity against breast carcinogenesis, we examined tumor development in K14-Tslptg, MMTV-PyMTtg, Il4r−/− (Tslp-PyMttg Il4rKO) in comparison to Tslp-PyMttg, PyMttg Il4rKO, and PyMttg animals. This evidence concerns the gene IL4R and neoplasm.