Complete response in disseminated EGFR-mutated lung adenocarcinoma through chemosensitivity-guided chemotherapy, osimertinib, and stereotactic ablative body radiotherapy: a case report

Background: Non-small cell lung cancer (NSCLC) harboring activating epidermal growth factor receptor (EGFR) mutations has undergone a therapeutic paradigm shift with the introduction of third-generation EGFR tyrosine kinase inhibitors (TKIs), particularly osimertinib. Despite these advances, disseminated disease remains challenging, and treatment selection for cytotoxic chemotherapy is still largely guideline-driven rather than individualized. Functional chemosensitivity testing using liquid biopsy-derived tumor cells represents an emerging strategy to personalize systemic therapy beyond molecular profiling alone. In addition, consolidative stereotactic ablative body radiotherapy (SABR) may enhance durable disease control after systemic response.

Case Description: We report the case of a 75-year-old woman diagnosed with stage IV disseminated lung adenocarcinoma involving mediastinal, cervical, and hilar lymph nodes, pleura, and bone. Molecular analysis revealed an EGFR exon 19 deletion, low programmed death-ligand 1 (PD-L1) expression (1%), and no other actionable alterations. A liquid biopsy-based chemosensitivity assay demonstrated marked tumor cell susceptibility to oxaliplatin and pemetrexed, guiding selection of a non-standard chemotherapy regimen. The patient received six cycles of oxaliplatin-pemetrexed in combination with continuous osimertinib (80 mg daily). Interim positron emission tomography combined with computed tomography (PET/CT) imaging showed near-complete metabolic regression of systemic disease. Residual activity within the primary lung lesion was subsequently treated with SABR, resulting in complete radiographic and metabolic remission. At 1-year follow-up, the patient remains disease-free on maintenance osimertinib alone, with minimal toxicity and preserved performance status.

Conclusions: This case illustrates the potential clinical value of integrating functional chemosensitivity testing with targeted therapy and consolidative SABR in disseminated EGFR-mutated NSCLC. Personalized chemotherapy selection based on tumor-specific drug responsiveness, rather than guideline-driven regimens alone, may contribute to exceptional treatment responses. These findings support further investigation of functional precision oncology approaches to optimize outcomes in advanced lung cancer.