CD109 and cancer: Since 2004 when Hashimoto et al. reported the expression of CD109 in human cancer,6 our group has earnestly investigated the immunohistochemical CD109 expression of tumor tissues, including that in lung and oral cancers,8, 9, 14, 15 and has performed biological analyses using CD109 transfected cells or transgenic mice.10, 11, 12, 16