Interpretation of p53 immunohistochemical stain of TP53-mutated myeloid neoplasms.

BACKGROUND: TP53 mutational status (TP53ms) is prognostically important in myeloid neoplasms. Immunohistochemistry (IHC) of p53 has been used as a surrogate for TP53 mutations, with faster results than next-generation sequencing (NGS) and cytogenetic analysis. Given the challenges posed by heterogeneous p53 IHC expression, this study aims to evaluate the interobserver interpretation of p53 stain as a surrogate marker for TP53m. METHODS: Fifty-three bone marrow (BM) specimens previously diagnosed as myeloid neoplasms or nonneoplastic BM specimens with available concurrent TP53ms were evaluated. p53 IHC staining was performed on all 53 core biopsy or clot sections. TP53 mutation was found in 24 cases (TP53m). Twenty-nine specimens were TP53 wild-type and served as the control group. Six hematopathologists (HPs) blinded to the diagnosis and TP53m independently scored the p53 staining pattern of the biopsies/clot sections for overall staining percentage (OSP) and staining intensity (dark staining percentage as a percentage of total cells (DCP)). RESULTS: The intraclass correlation was excellent for OSP (0.927) and good for DCP (0.848). For OSP, a cutoff of 30% resulted in sensitivity of 83.3%, specificity of 89.7%, PPV of 87.0%, and NPV of 86.7%. For DCP, a cutoff of 10% achieved sensitivity of 87.5%, specificity of 96.6%, PPV of 95.4%, and NPV of 90.3%. Additionally, DCP significantly correlated with the VAF of TP53m (R = 0.469, p = 0.028). CONCLUSION: High inter-rater reliability for OSP and DCP supports integrating p53 IHC into bone marrow evaluations for rapid TP53m assessment. With superior specificity and predictive values, DCP proves to be a more reliable diagnostic marker for TP53 mutations. While this approach shows promise for myeloid neoplasms, further validation is needed to overcome challenges and expand its clinical utility for tailored treatment strategies.