Application of Low-Dose Radiotherapy Combined with Immunotherapy for Drug-Resistant Hepatic Metastasis: a Case Series Analysis.

Objectives: There is no established standard regimen for end-stage patients suffering from multi-line refractory diffuse hepatic metastases. This case series intended to assess the antitumor activity, treatment tolerance and palliative value of whole-liver low-dose radiotherapy combined with PD-1 immunotherapy, with special attention paid to the occurrence of systemic abscopal effect. Patients and methods: This retrospective case series aimed to evaluate the clinical efficacy and safety of low-dose whole-liver radiotherapy (LDRT) combined with PD-1 inhibitor immunotherapy in patients with refractory diffuse hepatic metastases from solid tumors. Six patients who developed progressive diffuse hepatic metastases after one or more lines of prior systemic therapy and subsequently received LDRT plus immunotherapy were enrolled. All patients were followed up until the predefined cutoff date of July 2026. The primary endpoints were objective response rate (ORR) and the incidence of treatment-related adverse events (TRAEs). The secondary endpoints included symptomatic improvement and changes in quality of life. Tumor response was assessed according to the Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1, and adverse events were graded based on the Common Terminology Criteria for Adverse Events (CTCAE) version 5.0. All enrolled patients presented with extensive diffuse intrahepatic metastasis at baseline. Results: With a median follow-up of 7.5 months, tumor regression or radiological remission was observed in several patients,yielding an objective response rate (ORR) of 66.7%. Clinical symptomatic relief and improved quality of life were achieved in four patients after combination treatment. In terms of safety, No grade 3 or higher TRAEs definitively attributable to this combined regimen were observed during treatment.The combined regimen appeared to be generally tolerable for the liver. Collectively, these preliminary findings suggest a potential clinical benefit and acceptable safety of this LDRT plus immunotherapy combination in one or more lines pretreated patients with diffuse hepatic metastases. Conclusion: This exploratory case-series generates the hypothesis that low-dose radiotherapy combined with immunotherapy may yield clinical benefits for selected patients with diffuse treatment-refractory hepatic metastases. Further prospective clinical trials and translational research are warranted to elucidate the underlying immunomodulatory mechanisms and define patient subsets most likely to derive clinical benefit from this approach.