p53 immunohistochemistry staining is a rapid screening method for TP53 mutation in myeloid malignancies suitable for integration into routine diagnostic laboratory practice.

TP53 mutations are a recognised poor prognostic marker across myeloid malignancies associated with inferior overall survival. Immunohistochemistry (IHC) for p53 represents a promising adjunctive test with rapid turn-around; however, controversy exists around its utility and optimal positive staining threshold. The aims of this study were to determine the diagnostic testing characteristics and optimal threshold of positive staining for p53 IHC in comparison to next-generation sequencing (NGS) results across myeloid malignancies and compare haematopathologist review to digital analysis. A total of 117 bone marrow samples, including TP53 wild-type (n=50) and TP53 mutant (n=67) based on NGS results, were independently assessed by two blinded haematopathologists and analysed using image analysis software with reliability assessment. A receiver operating characteristic curve was used to determine the optimal cut-off for predicting TP53 mutation. There was high reliability between reviewers [intraclass correlation (ICC) 0.84; confidence interval (CI) 0.783-0.891] and between average reviewer and analysis software (ICC 0.794; CI 0.715-0.853). The area under the curve was similar (p=0.818) for computer versus average reviewer. The optimal cut-off for reviewer assessment was 2% strong positive staining with adequate sensitivity (70%) and specificity (90%). p53 IHC has adequate test characteristics to be considered as a rapid screen to identify cases of TP53 mutation. Issues remain in identifying truncating and some splicing mutations.