Objective:

To investigate the clinical-pathological features, immunophenotype, and diagnostic criteria of metaplastic thymoma (MT) and distinguish it from pulmonary mucoepidermoid carcinoma (PEMC).

Approach:

• Case Study: Clinical data from a single patient with surgically confirmed metaplastic thymoma were collected, including histological examination, immunohistochemical staining, and molecular testing.

Key Findings:

• Thepatientwasamiddle-agedwomanwithrecurrentchesttightnessandamisdiagnosisofpulmonarymucoepidermoidcarcinoma.Postoperativepathologicalanalysisrevealedatumorwithbenignepithelioidandspindlecells,characterizedbyspecificimmunohistochemicalmarkers:CD117(–),CD20(–),CD3(speckled+),CD34(–),CD5(speckled+),CD99(–),CK20(–),CK7(partial+),EMA(spindlecells+;epithelioidcellsspeckledperinuclearly+),Ki67(5%+),P53(80%+),P63(+),Syn(–),TDT(–).MoleculartestingdetectedYAP1-MAML2genebreak-uprearrangement.

Interpretation:

Metaplastic thymoma is a rare subtype of thymoma that requires careful integration of clinical, histological, immunohistochemical, and molecular data for accurate diagnosis.

Limitations:

• Thestudyisbasedonasinglecase,whichlimitsthegeneralizabilityofthefindingsandmayintroducepotentialdiagnosticbiasorinaccuraciesinbiopsysampling.

Conclusion:

Accurate diagnosis of metaplastic thymoma necessitates a comprehensive approach that includes clinical presentation, microscopic morphology, immunohistochemical features, and molecular biology data.