Detection of TP53 mutations by immunohistochemistry in acute myeloid leukemia varies with interpreter expertise and mutation status.

OBJECTIVE: TP53 mutations, including missense and inactivating (frameshift, splice site, and nonsense) mutations, occur in approximately 10% of myeloid neoplasms and confer adverse outcomes. Classification of myeloid neoplasms by World Health Organization and International Consensus Classification standards recognizes the importance of early detection of TP53 mutations. p53 immunohistochemistry (IHC) is a widely accessible method used to detect mutations; however, previous studies have demonstrated variable accuracy, especially for inactivating TP53 mutations. Recently, sequencing using targeted panels has seen increased use. Although highly accurate, sequencing is resource intensive and not universally available.

METHODS: Using 134 bone marrow samples from patients with acute myeloid leukemia evaluated for TP53 mutation by sequencing, we assessed the concordance of p53 IHC with sequencing as well as the interrater-reliability for IHC intensity and percent positivity.

RESULTS: Consistent with previous studies, we found that p53 IHC was strongly specific and modestly sensitive for missense mutations and that overall performance improved with dedicated hematopathology training. We also found that IHC performed poorly for inactivating mutations and was even variable between cases harboring identical amino acid changes. Low predicted transcriptional activity of p53 missense proteins correlated with a mutant pattern of IHC staining. The status of the second allele and variant allele frequency also affected the accuracy of p53 IHC as a surrogate for TP53 allele status.

CONCLUSION: Cases of acute myeloid leukemia with TP53 mutations predicted to have low transcriptional activity showed reduced overall survival. Our results demonstrate limited practical utility of p53 IHC for accurate evaluation of TP53 mutation status because of multifactorial confounders.