A similar role for STAT3 in growth arrest has been identified in monocytes.40 In addition, in T-lymphocytes, STAT3 inhibits the proliferative response to IL-2,54 whereas IL6-mediated activation of STAT3 inhibits hepatocyte proliferation55 and growth of carcinoma and myeloid leukemia cells.40 As the percentage of Ki67+β-cells did not increase in PDL head of pancreas in Stat3−/− mice, cytokines or growth factors produced locally in PDL tail may signal via STAT3 and prevent excessive β-cell proliferation specifically in PDL tail. Here, MKI67 is linked to carcinoma.