To gain insight into the mechanism underlying the ability of hTS to promote tumorigenesis in Men1-null mice, we performed IHC analysis to examine p21Cip1, p18INK4c, and p27Kip1 expression in PanNET tissues isolated from hTS/Men1+/ΔN3-8 mice (n = 5; 2 adenoma and 3 carcinoma) compared with control PanNET tissues isolated from Men1+/ΔN3-8 mice (n = 1; adenoma). This evidence concerns the gene CDKN1A and adenoma.