Peritoneal Metastasis in Advanced Lung Adenocarcinoma Harboring EGFR Exon 19 Deletion/T790M with STRN::ALK Fusion and EGFR Kinase Domain Duplication: Two Case Reports and a Narrative Literature Summary.

Peritoneal metastasis from lung adenocarcinoma is rare and generally associated with poor prognosis. Here, we report two cases of advanced NSCLC with multiple metastases in which the patients developed rare peritoneal metastases during disease progression. Next-generation sequencing (NGS) revealed rare genomic alterations: one patient harbored concurrent EGFR exon 19 deletion and T790M mutation, accompanied by EGFR amplification, TP53 mutation, and STRN::ALK fusion, while the other exhibited EGFR kinase domain duplication and TP53 mutation. Both patients underwent multiple lines of systemic therapy, including targeted treatment guided by NGS results, and achieved survival exceeding six months following the diagnosis of peritoneal metastasis, with ongoing treatment at last follow-up. These observations suggest that more precise molecularly guided targeted therapy may play a crucial role in the clinical management of peritoneal metastasis.