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

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 both the World Health Organization and the International Consensus Classification standards now recognize the prognostic and therapeutic importance of early detection of TP53 mutations. p53 immunohistochemistry (IHC) is a simple and rapid method commonly used to detect p53 mutations. More recently, sequencing via targeted panels has also seen increased use. While highly accurate, sequencing is resource intensive and not universally available. IHC represents a more accessible option for mutation detection, however previous studies have demonstrated variable accuracy, especially for inactivating TP53 mutations. Using 134 bone marrow core samples of acute myeloid leukemia (AML) evaluated for TP53 mutation by a sequencing panel, we assessed the concordance of p53 IHC with sequencing as well as the inter-rater reliability for IHC intensity and percent positivity. 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 TP53 missense mutations correlated with a mutant pattern of IHC staining. The status of the second allele in missense mutations and variant allele fraction also affected the accuracy of p53 IHC as a surrogate for TP53 allele status. AMLs expressing p53 mutations that were predicted to have low transcriptional activity correlated with reduced overall survival. Our results demonstrate limited practical utility of p53 immunohistochemistry for accurate evaluation of TP53 mutation status due to multifactorial confounders.