Rhabdoid large cell carcinoma of lung, with illustrative immunohistochemical and molecular findings.

Large cell carcinomas with rhabdoid phenotype (LCC-RP) account for <1% of pulmonary large cell carcinomas and are associated with extremely poor prognosis. We report a case of a 64-year-old male patient who presented at an advanced stage with a LCC-RP, arising from a poorly differentiated adenocarcinoma of the lung. Ninety percent of the tumor consisted of large pleomorphic rhabdoid tumor cells that showed eosinophilic cytoplasmic inclusions and the remaining 10% showed evidence of adenomatous differentiation. Rhabdoid areas were immunohistochemically positive for pan-cytokeratin AE1/3, epithelial membrane antigen, vimentin, thyroid transcription factor-1, integrase interactor-1, and negative for desmin. Nuclear positivity was absent for Myo-D1. The parent adenocarcinoma was positive for thyroid transcription factor-1 and cytokeratins 7. Epidermal growth factor receptor mutation analysis revealed the same mutation (p.delL747-T751) in both areas, suggesting that the malignant rhabdoid phenotype represents a dedifferentiation phenomenon of the adenocarcinoma. This is the first reported case of an Exon 19 deletion in epidermal growth factor receptor of the activating type detected in a LCC-RP associated with a poorly differentiated pulmonary adenocarcinoma.