Mutations of the TP53 Gene Occur in 13.4% of Acute Myeloid Leukemia and Are Strongly Associated with a Complex Aberrant Karyotype.

The TP53 gene is the most frequently mutated gene in human tumors identified so far. In a prior study we demonstrated that 78% of AML with complex aberrant karyotype show a mutation of the TP53 gene. The aim of this study was to determine the frequency of TP53 mutations in an unselected cohort of AML and to analyze the relation to cytogenetic and molecular genetic aberrations. In total 149 AML cases were examined by chromosome banding analysis and screened for FLT3-length mutations (FLT3-LM), MLL partial tandem duplication (MLL-PTD), NPM1 mutations, and TP53 mutations. The cohort included cases with t(8;21) (n=10), t(15;17) (n=6), inv(16) (n=4), 11q23/MLL-rearrangement (n=6), trisomy 8 sole (n=13), AML with normal karyotype (n=46), AML with complex aberrant karyotype defined as showing 3 and more clonal abnormalities but no balanced rearrangement leading to a leukemia specific fusion gene (n=26), and AML with other abnormalities (n=38). FLT3-LM were observed in 21, MLL-PTD in 4, and NPM1-Mutations in 26 cases. TP53 mutation screening of exons 3–9 was performed by denaturing high performance liquid chromatography (DHPLC). All mutations detected were verified by direct sequencing. Overall, TP53 mutations were detected in 20 of the 149 cases (13.4%). Within this cohort of TP53 mutated cases, coincidences of FLT3-LM and MLL-PTD, respectively, with TP53 mutation were detected in one case each. A complex aberrant karyotype was present in 17 of 20 cases (85%) with TP53 mutation. The remaining 3 cases with TP53 mutation showed a normal karyotype, a trisomy 8, and t(8;21) as the sole abnormality, respectively. Therefore, we confirmed a high incidence of TP53 mutations in AML with complex aberrant karyotype (17/26, 65.4%). On the other hand TP53 mutations are very rare in AML without a complex aberrant karyotype (3/123, 2.4%). Furthermore, we divided AML with complex aberrant karyotype into two subgroups:

1. AML with “typical” complex aberrant karyotype showing a deletion of at least one of the following regions: 5q31, 7q31, 17p13 (definition according to Schoch et al. GCC, 2005) and

2. AML with “untypical” complex aberrant karyotype comprizing all others.

Interestingly, the frequency of TP53 mutations within the “typical” complex aberrant karyotype group was 75% (15/20) while in the “untypical” group it was 33% (2/6) (p=0.138). In conclusion, the overall incidence of TP53 mutations is low in AML. TP53 mutations are highly associated with AML and complex aberrant karyotype and occur very infrequently in all other cytogenetic subgroups (p<0.001). They occur frequently in particular in the subgroup showing a typical pattern of chromosomal deletions (5q, 7q, 17p). TP53 mutations might explain in part the chemoresistance of AML with complex aberrant karyotype. In addition to cytogenetics a rapid diagnostic screening for TP53 mutations could be a valuable tool to identify a subgroup of AML with poor prognosis. This would allow the early assignment of patients to alternative treatment strategies using also options targeting the TP53 pathway.