Correlation between TP53 mutational status and digital quantification of p53 immunohistochemistry in mantle cell lymphoma.

TP53 mutation is a significant negative prognostic factor in mantle cell lymphoma (MCL). While p53 immunohistochemical (IHC) staining is frequently used to evaluate TP53 mutation status, specific cut-offs correlating with mutations remain undefined and largely empirical. This study analyzed tumor specimens from 172 patients with MCL with both p53 IHC and TP53 mutation data, categorizing p53 nuclear expression into four groups (0 + , 1 + , 2 + , and 3 +) using digital image analysis. We established IHC cut-offs with 100% specificity for identifying TP53 non-truncating mutations: 5% for 3 + nuclei, 50% for combined 2 + and 3 + nuclei, and an H-score of 150. The combined 2 + and 3 + nuclei percentage showed the highest sensitivity and negative predictive value. Notably, p53 IHC expression did not significantly correlate with the variant allele frequencies (VAFs) of TP53 missense mutations. However, patients with both TP53 missense and ATM mutations displayed lower p53 expression compared to those with only TP53 missense mutations. TP53 truncating mutations affecting the DNA-binding domain were associated with null p53 staining, while truncating mutations in the tetramerization domain showed weak to moderate staining. Cases with single nucleotide substitutions involving TP53 splice sites showed weak to moderate p53 staining and lacked 3 + nuclei. In cases where multiple types of TP53 mutations coexisted, the clonally dominant mutation influenced the overall p53 expression level. Finally, we observed significantly worse overall survival in patients demonstrating p53 overexpression by using the above mentioned IHC cut-offs. This study provides essential evidence for interpreting p53 IHC staining and may potentially guide rapid risk stratification of patients with MCL, especially in limited resource settings.