We examined also the frequencies of FoxP3+ Tregs in the tumors of these mice because Tregs are implicated in the regulation of anti‐tumor immune responses.[4a] Despite small differences, such as an increase in RARα‐KO in MC38 tumors and a decrease in RARα‐TG in B16 tumors, Treg frequencies among CD4 T cells in the dLN and tumors of RARα‐KO and RARα‐TG were largely comparable (Figure S6A,B, Supporting Information). This evidence concerns the gene FOXP3 and neoplasm.