AML patients with CEBPα mutations mostly retain identical mutant patterns but frequently change in allelic distribution at relapse: a comparative analysis on paired diagnosis and relapse samples

The roles of CEBPalpha mutations and its cooperating mutations in the relapse of acute myeloid leukemia (AML) are not clear. CEBPalpha mutations were analyzed on 149 patients with de novo AML at both diagnosis and relapse. Twenty-two patients (14.8%) had the mutations at diagnosis, two patients had N-terminal nonsense mutations alone, one had homozygous inframe duplication at the bZIP domain, and 19 patients had both N-terminal and bZIP mutations. Twenty patients relapsed with identical mutant patterns, two lost CEBPalpha mutations and none acquired the mutations at relapse. Cloning analysis showed that the N-terminal and C-terminal mutations occurred on separate cloned alleles and also on the same alleles in most of the diagnosis and relapse samples. Losing one of the two or more mutations on the same allele or acquiring the other mutation on the allele original carrying single mutation were observed not infrequently in the paired samples analyzed. Seven patients with CEBPalpha mutations had cooperating mutations with FLT3/ITD, FLT3/TKD or N-ras but not K-ras mutations. Our study showed that 91% of de novo AML harboring CEBPalpha mutations at diagnosis retained the identical mutant patterns but frequently changed in the allelic distribution at relapse.