Histological transformation into pulmonary sarcomatoid carcinoma from lung adenosquamous carcinoma after radical resection of EGFR gene Exon-21 L858R mutation: a case report and literature review.

Pulmonary sarcomatoid carcinoma (PSC) is frequently underdiagnosed or misdiagnosed due to its rarity and complex histological features. To date, no universally recommended treatment regimens have been established for this rare subtype, and clinical management is currently extrapolated primarily from standard non-small cell lung cancer (NSCLC) protocols. Herein, we report a case of PSC initially diagnosed as multiple primary lung cancer, including adenosquamous carcinoma and adenocarcinoma (pT1N0M0, IA stage, EGFR Exon-21 L858R mutation, below the detection limit) and adenocarcinoma (pT2aN0M0, stage IB, EGFR Exon-21 L858R mutation). Despite radical surgical resection followed by targeted therapy with afatinib (30 mg orally once daily), the disease recurred. Repeat biopsy confirmed the diagnosis of PSC secondary to histological transformation. The patient achieved a durable complete response (CR) to combined immunochemotherapy. We further review the existing literature on EGFR-TKI-associated histological transformation in lung cancer, to provide guidance for the clinical management of this challenging clinical scenario.