Studies of the gut–liver axis have enhanced our understanding of the pathophysiology of various liver diseases and the mechanisms underlying the regulation of the effectiveness of therapies. Radiotherapy (RT) is an important therapeutic option for patients with unresectable hepatocellular carcinoma (HCC). However, the role of the microbiome in regulating the response to RT remains unclear. The present study characterizes the gut microbiome of patients responsive or non-responsive to RT and investigates the molecular mechanisms underlying the differences in patient response. We collected fecal samples for 16S rRNA sequencing from a prospective longitudinal trial of 24 HCC patients receiving RT. We used fecal microbiota transplantation (FMT), flow cytometry, and transcriptome sequencing to explore the effects of dysbiosis on RT. We also examined the role of stimulator of interferon genes (STING) in RT-associated antitumor immune responses mediated by gut microbiota in STING- (Tmem173^−/−) and cGAS-knockout (Mb21d1^–/–) mouse models. We propose that primary resistance to RT could be attributed to the disruption of the gut microbiome. Mechanistically, gut microbiome dysbiosis impairs antitumor immune responses by suppressing antigen presentation and inhibiting effector T cell functions through the cGAS–STING–IFN-I pathway. Cyclic-di-AMP – an emerging second messenger of bacteria – may act as a STING agonist and is thus a potential target for the prediction and modulation of responses to RT in HCC patients. Our study highlights the therapeutic potential of modulating the gut microbiome in HCC patients receiving RT and provides a new strategy for the radiosensitization of liver cancer.

To investigate the potential impact of fractionation regimes and overall treatment time (OTT) on lymphopenia during definitive radiotherapy (RT) and its associations with patient outcomes in non-small cell lung cancer (NSCLC). Subjects consisted of 115 patients who had received definitive chemoradiation therapy (CRT) with different doses and fractions for unresectable stage III NSCLC. Clinical and laboratory records were reviewed to assess the changes in total lymphocyte counts (TLCs) during definitive RT. The associations of the TLCs with the clinical and treatment features, and outcomes were analyzed. The median reduction of TLCs in the entire cohort was 1300 cells/μL (interquartile range [IQR], 950–1510 cells/μL). Of all patients, 63 (54.8%) experienced severe lymphopenia (SL) (TLC nadir < 500 cells/μL), which occurred at a median of the 5th week following RT initiation, not at the completion of RT or upon treatment with maximal doses. SL risk was increased over the first 5 weeks (odds ratio [OR] = 3.455, P = 0.007), after which, no increased risk was observed (OR = 0.562, P = 0.216). The median TLCs remained low and failed to recover to the initial normal values of their pre-RT level after 2 months of RT completion. Patients without SL exhibited significantly improved progression-free survival (hazard ratio [HR] = 0.544, P = 0.010) and overall survival (HR = 0.463, P = 0.011) after controlling for confounding variables in multivariate analyses. The incidence of SL was significantly lower (71.1% reduction in risk (OR = 0.289, P = 0.007)) in patients who received hypofractionated RT with an OTT within 4 weeks, compared to those who had an OTT of more than 4 weeks (32.1% vs 62.1%, P = 0.006). Multivariate analyses revealed that OTT within 4 weeks (OR = 0.322, P = 0.032) was significantly associated with a decreased risk of developing SL after controlling for confounding factors. Hypofractionated RT was significantly associated with a decreased risk of SL and improved survival during definitive radiotherapy for unresectable stage III NSCLC.