Correlating p53 immunostaining patterns with somatic TP53 mutation and functional properties of mutant p53 in triple-negative breast cancer

Abstract

Aims: Immunohistochemical (IHC) staining of p53 is a potential marker for TP53 mutations in various cancers. However, criteria for predicting TP53 mutations in triple-negative breast cancer (TNBC) using p53 IHC staining are not yet established. We aim to correlate p53 IHC expression patterns with TP53 mutation status in TNBC.

Methods and results: A total of 113 TNBC cases were analysed for p53 IHC staining pattern and somatic TP53 mutation using whole-exome sequencing. Functional properties of TP53 mutations were determined using the National Cancer Institute (NCI) TP53 database. P53 IHC patterns were categorized as nuclear overexpression (n = 58), null pattern (n = 40), wildtype (n = 15), cytoplasmic (n = 5), and subclonal (n = 5). The cutoff for predictive p53 nuclear overexpression was determined to be 80%, which strongly correlated with TP53 mutations. Notably, p53 overexpression had a positive predictive value (PPV) of 83% for missense or in-frame mutations, while the null pattern showed a PPV of 85% for detecting nonsense, frameshift, or splicing mutations. P53 overexpression was significantly linked to missense mutations within the DNA-binding domain (DBD) exhibiting gain-of-function (GOF) or dominant-negative effect (DNE). Cases exhibiting cytoplasmic expression correlated with nonsense or frameshift mutations in the DBD, nuclear localization signal (NLS), or splice sites. Cases with subclonal p53 staining patterns were associated with TP53 mutations.

Conclusion: Our study proposes newly defined criteria for interpreting p53 immunostaining patterns in TNBC, potentially allowing for the prediction of TP53 mutation types and their functional implications.

Keywords: TP53 mutation; gain‐of‐function; mutant p53; p53 expression; p53 immunohistochemistry; triple‐negative breast cancer.

Figure 1

Representative patterns of p53 immunohistochemical staining in triple‐negative breast cancer. (A) Overexpression pattern of p53 in more than 80% of tumour cells with strong nuclear expression. (B) Complete loss of staining (null pattern). (C) Wildtype pattern with variable and patchy nuclear expression.

Figure 2

Lollipop plot depicting the frequency and position of TP53 mutations based on p53 immunohistochemical staining patterns. Localization of TP53 mutation in (A) p53 overexpression (n = 60) and (B) p53 null pattern (n = 40).

Figure 3

Distribution of p53 immunohistochemical staining patterns and TP53 alteration in triple‐negative breast cancer. The oncoplot presents TP53 status, including mutation parameters, functional properties, and copy number variations, according to p53 staining patterns. CNV, copy number variation; DBD, DNA‐binding domain; GOF, gain‐of‐function; LOH, loss of heterozygosity; NA, not available; NE, no evidence of functional property; NES, nuclear export signal; NLS, nuclear localization signal; PRD, proline‐rich domain; TAD, transactivation domain.

Figure 4

Cytoplasmic p53 staining patterns and a lollipop plot of TP53 mutations. (A) Case with moderate to strong cytoplasmic and nuclear staining harbouring TP53 nonsense mutation, R342*. (B) Case with weak cytoplasmic expression and the absence of nuclear expression harbouring TP53 frameshift deletion, S261Vfs*84. (C) TP53 mutation frequency and position in the four cases with cytoplasmic expression, excluding one splicing mutation for which the domain location was not available.

Figure 5

Representative cases with subclonal p53 staining patterns. (A) Case exhibiting a subclonal pattern with a combination of p53 overexpression (arrow) and wildtype pattern (arrowhead) with a TP53 missense mutation, M237I in DNA‐binding domain. (B) Case displaying overexpression (arrow) and wildtype (arrowhead) patterns with cytoplasmic expression harbouring a TP53 frameshift deletion, P301Qfs44, near the nuclear localization signal. (C) Case with a subclonal pattern showing a combination of wildtype (arrowhead) and null pattern (arrow) harbouring a TP53 frameshift deletion, E343Gfs2, near the nuclear export signal domain. (D) Case with a mixture of wildtype (white arrow), null (black arrow), and overexpression (arrowhead) harbouring a TP53 nonsense mutation, S94* near the proline‐rich domain.