Correlation of TP53 Genetic Alterations with p53 Immunohistochemical Expression and Their Prognostic Significance in DLBCL

<i>TP53</i> genetic alterations represent a critical molecular feature in diffuse large B-cell lymphoma (DLBCL), with well-established associations with aggressive disease behavior and therapeutic resistance. However, significant controversy persists regarding the clinical utility of p53 immunohistochemical (IHC) expression as a surrogate marker. This study presents a thorough investigation of <i>TP53</i> genetic alterations and their correlation with p53 protein expression in 664 cases of DLBCL. Using targeted next-generation sequencing (tNGS), we identified <i>TP53</i> alterations (mutations and/or copy number losses (CNLs)) in 170 cases (25.6%). Among them, 161 cases had mutations. Concurrent analysis of copy number variations (CNVs) in 109 cases revealed <i>TP53</i> CNLs in 17.4% (19/109), with 68.4% (13/19) of these showing coexisting mutations. Immunohistochemical evaluation of p53 expression in 371 cases demonstrated strong positivity (≥65% cells) in 21% (78/371), complete negativity (<1%) in 5.7% (21/371), and wild-type pattern (1-65%) in 73.3% (272/371) of cases. The p53 IHC laboratory-developed test (LDT) showed 79.2% sensitivity and 91.6% specificity for detecting <i>TP53</i> alterations overall, though sensitivity varied significantly by mutation type: 86.2% for missense mutations but only 14.3% for nonsense mutations. Clinically, cases with <i>TP53</i> alterations exhibited more aggressive disease characteristics, including higher ECOG performance scores, increased frequency of B symptoms, and poorer initial treatment responses (complete response rate 68.3% vs. 82.5% in wild-type cases). Most importantly, <i>TP53</i> genetic alterations, but not p53 protein expression patterns, emerged as an independent prognostic factor for progression-free survival. Our findings demonstrate that tNGS effectively identifies most <i>TP53</i> alterations and complementary CNV analysis enhances detection of copy number losses. The p53 IHC LDT serves as a useful but imperfect screening tool, with high specificity but variable sensitivity depending on mutation types. These results have important implications for molecular diagnostics in DLBCL, supporting the necessity for comprehensive genetic testing rather than reliance on protein expression analysis alone for accurate risk stratification and treatment planning.