Novel strategy of pemetrexed combined with localized therapy: breakthrough impact of long-term maintenance regimen on patient survival—a case report

The outcomes of untreated patients with lung adenocarcinoma with brain metastasis are poor; the usual survival period was around weeks to 3 months. While molecularly targeted agents and immune checkpoint inhibitors demonstrate survival benefits in selected populations, significant access barriers persist, particularly among socioeconomically disadvantaged groups. This report details exceptional survival duration in a KRAS p.Q61H/TP53 co-mutant case, exceeding conventional survival estimates and necessitating strategies to overcome system-level care constraints. A male Asian patient aged 70–80 years presented with bilateral pulmonary lobe lesions (largest: 57 mm in left inferior lobe) and a 14-mm right frontal lobe metastasis. Histopathological and immunohistochemical analysis confirmed stage IV pulmonary adenocarcinoma, with genomic testing revealing co-mutations in KRAS exon 3 c.183A > C (p.Q61H) and TP53 exon 7 c.738G > A (p.R247K). The patient received pemetrexed–cisplatin chemotherapy, radiotherapy, and palliative surgery. Mild adverse events (drug eruption, elevated blood glucose, transient creatinine abnormalities) were resolved with symptomatic management. Patient experienced a confirmed partial response after follow-up for at least 5 years. This case demonstrates unprecedented long-term survival in a patient with KRAS p.Q61H/TP53 c.G738A-mutant lung adenocarcinoma and brain metastasis treated with pemetrexed-based maintenance therapy combined with local interventions. The regimen showed efficacy, safety, and cost-effectiveness, offering a viable strategy for resource-limited settings.