Performance of the pattern‐based interpretation of p53 immunohistochemistry as a surrogate for TP53 mutations in vulvar squamous cell carcinoma

Abstract

Aims The most commonly mutated gene in vulvar squamous cell carcinoma (VSCC) is TP53 and its prognostic value, particularly in HPV‐independent VSCC, is uncertain. In other tumours, p53 immunohistochemistry (IHC) is an excellent surrogate marker for TP53 mutations. In order to study this in VSCC, we assigned six p53 IHC patterns into two final classes: ‘wild‐type’ or ‘mutant’. We determined the performance and interobserver variability of this pattern‐based p53 IHC approach. Methods and results Two experienced gynaecological pathologists scored the predefined p53 IHC patterns of 59 VSCC, independently and blinded for molecular data. Agreement was calculated by Cohen's kappa. All disagreements regarding p53 IHC patterns were resolved by a consensus meeting. After DNA isolation, the presence of pathogenic TP53 variants was determined by next‐generation sequencing (NGS). Sensitivity, specificity and accuracy of p53 IHC as a surrogate marker for TP53 mutation status were calculated. Initial p53 IHC pattern interpretation showed substantial agreement between both observers ( k = 0.71, P < 0.001). After consensus, 18 cases (30.5%) were assigned a final p53 IHC class as TP53 wild‐type and 41 cases (69.5%) as mutant. The accuracy between the p53 IHC class and TP53 mutation status, after the consensus meeting, was 96.6%. Moreover, the sensitivity and specificity were high 95.3% [95% confidence interval (CI) = 82.9–99.1% and 100% (95% CI = 75.9–100%)]. Conclusions Pattern‐based p53 IHC classification is highly reproducible among experienced gynaecological pathologists and accurately reflects TP53 mutations in VSCC. This approach to p53 IHC interpretation offers guidance and provides necessary clarity for resolving the proposed prognostic relevance of final p53 IHC class within HPV‐independent VSCC.

Comparison of p53 immunohistochemical staining in differentiated vulvar intraepithelial neoplasia (dVIN) with that in inflammatory dermatoses and benign squamous lesions in the vulva

“…and Kortekaas et al . have demonstrated that p53 IHC is an excellent surrogate for TP53 mutational status when a pattern‐based framework, the same framework that we have used in this study, is used 44,45 . In this pattern‐based framework, there were four mutational IHC patterns [basal overexpression, parabasal/diffuse overexpression, absent (null), and cytoplasmic].…”

“…The low rates of p53 aberrations in dVIN are more likely to be attributable to historically poor reproducibility in diagnosing dVIN and assessing p53 patterns. In the light of recent studies that have directly correlated p53 staining patterns and TP53 mutation status, 44,45 we are able to re‐evaluate the utility of p53 IHC from a new perspective. We recognise, like Liegl et al ., that p53 can be up‐regulated in inflammatory lesions, owing to ischaemic stress resulting from poor oxygenation, vascular alterations, and inflammation 47 .…”

“…In the future, study of lesions with ambiguous morphology, dVIN diagnoses on small biopsies, blinded assessment of p53 patterns and correlation of these with underlying TP53 mutational data would be beneficial next steps. We did not include any HPV‐related lesions, which can produce a basal‐sparing pattern 19,44,45,51 . We also acknowledge that p53 staining protocols may differ widely between laboratories and that, as a result, interpretative issues can arise.…”

“…Most recently, Tessier-Cloutier et al and Kortekaas et al have demonstrated that p53 IHC is an excellent surrogate for TP53 mutational status when a pattern-based framework, the same framework that we have used in this study, is used. 44,45 In this patternbased framework, there were four mutational IHC patterns [basal overexpression, parabasal/diffuse overexpression, absent (null), and cytoplasmic]. The basal overexpression pattern (uniform strong staining of at least 80% of the basal cells without significant parabasal staining) is of interest.…”

“…We did not include any HPVrelated lesions, which can produce a basal-sparing pattern. 19,44,45,51 We also acknowledge that p53 staining protocols may differ widely between laboratories and that, as a result, interpretative issues can arise. Overtitrated p53 IHC can make the distinction between uniform and patchy staining difficult or nearly impossible in some laboratories.…”