“…In myeloid leukemia the chronic phase is characterized by loss of proliferation control but maintenance of di erentiation capacity, while the conversion to the acute, blastic phase is associated with loss of di erentiation capacity (Champlin and Golde, 1985) and, in 50 ± 60% of the cases, mutation in the TP53 gene (Feinstein et al, 1991). In thyroid, the relatively benign, well di erentiated carcinomas do not present TP53 mutations, which are only found in the aggressive, anaplastic forms (Wright et al, 1991, reviewed in Fagin, 1994. Interestingly, a similar correlation has been also found in p53 knock-out mice where chromosomal abnormalities and anaplastic phenotypes are more frequent and severe in p53 7/7 mice than in wild type mice (Kemp et al, 1993;Venkatachalam et al, 1998).…”