YAP1 and β-Catenin Immunohistochemistry as a Surrogate Marker for GTF2I-Mutant Type A/AB Thymomas.

Cohort studyModern pathology : an official journal of the United States and Canadian Academy of Pathology, Inc· Aug 2026

YAP1 and β-Catenin Immunohistochemistry as a Surrogate Marker for GTF2I-Mutant Type A/AB Thymomas.

Nicholas Frazzette, Jonathan Willner, Luis Chiriboga … Andre L Moreira

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Thoracic PathologyCohort studyDiagnosisQ1IF 6.6

Cytoplasmic β-catenin staining is highly specific for indolent type A/AB thymomas.

YAP1 and β-Catenin Immunohistochemistry as a Surrogate Marker for GTF2I-Mutant Type A/AB Thymomas.

Nicholas Frazzette … Andre L Moreira

Modern pathology · Aug 2026 · Q1 in Pathology

Background

Thymomas are rare thymic epithelial tumors classified by the World Health Organization into type A/AB thymomas, which commonly harbor GTF2I mutations and behave indolently, and type B thymomas and thymic carcinomas, in which these mutations are less common.

Methods

We analyzed the TCGA thymoma dataset and an institutional cohort of 38 thymic epithelial tumors to evaluate YAP1 and β-catenin immunohistochemistry (immunohistochemistry) as surrogate markers for GTF2I mutation status and histologic classification.

n = 38 thymic epithelial tumors

Results

94%

Cytoplasmic β-catenin correctly identified indolent thymomas 94% of the time when present.

n = 38 thymic epithelial tumors

More results

Type A and AB thymomas are uniquely enriched for a recurrent somatic hotspot mutation in GTF2I (p.

In the TCGA dataset, YAP1 and CTNNB1 mRNA expression were markedly elevated in type A/AB thymomas relative to type B and carcinoma subtypes, and GTF2I-mutant tumors exhibited significantly higher YAP1 mRNA expression than GTF2I-wildtype tumors.

More results

Targeted next-generation sequencing of our institutional cohort confirmed enrichment of the canonical GTF2I p.

L424H hotspot in indolent subtypes.

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Conclusion

These findings implicate crosstalk between Hippo and Wnt signaling in GTF2I-mutant thymomas and position YAP1 and β-catenin immunohistochemistry as accessible, cost-effective surrogates for molecular subtyping in a tumor where standard sequencing panels have limited coverage.

YAP1 and β-Catenin Immunohistochemistry as a Surrogate Marker for GTF2I-Mutant Type A/AB Thymomas.

YAP1 and β-Catenin Immunohistochemistry as a Surrogate Marker for GTF2I-Mutant Type A/AB Thymomas.

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