CCND1 and cancer: Loss of expression including loss of heterozygosity or promoter methylation of the BTG family genes have been reported in different types of cancers.11, 12, 13, 35, 36, 37 Knockout mouse models for BTG3 and Tob were established,27, 38 which either succumbed to lung tumors at an old age in the case of Btg3 knockouts27 or spontaneously developed a variety of tumors in the case of Tob knockouts.38 Although increased cyclin D1 expression was implicated in tumor formation in the Tob-null mice, it was not clear why Btg3 deficiency caused lung tumors in mice.