In mice, homozygous disruption of Tsc1 or Tsc2 is lethal during embryogenesis, and heterozygous Tsc1+/− and Tsc2+/− mice develop renal cystadenomas, liver hemangiomas, and infrequently, paw angiosarcomas (Kobayashi et al., 1999; Onda et al., 1999; Kobayashi et al., 2001; Kwiatkowski et al., 2002). Here, TSC2 is linked to angiosarcoma.