High dietary fiber is associated with improved outcomes in patients with melanoma and sarcoma treated with immunotherapy regardless of gut microbiome dysbiosis and social vulnerability

Background: Social vulnerability, dietary fiber, and the gut microbiome have been individually implicated in clinical outcomes for melanoma and sarcoma patients. This study hypothesized that increasing social vulnerability is associated with insufficient dietary fiber intake and negatively associated with microbiome composition and clinical outcomes. Methods: Clinicopathologic data, baseline fiber intake, and gut microbiome profiles were assessed in 153 patients with melanoma or sarcoma treated with immune checkpoint blockade (ICB) and prospectively followed. Patients’ social vulnerability index (SVI) and fiber intake were evaluated for associations with microbiome composition, treatment response, and overall survival (OS). Results: SVI percentile was 0.4 (interquartile ratio [IQR], 0.2–0.7), and median dietary fiber intake was 17 (IQR, 15–20) g/day. SVI was inversely correlated with dietary fiber intake (r, −0.18, p =.0398). Gut microbiome analyses revealed community and compositional differences by SVI, including inverse associations with α-diversity and the relative abundance of favorable bacteria such as Bifidobacterium longum (p <.001), contrasting the positive associations observed between fiber and these microbial markers. Increased dietary fiber intake was associated with measurable response to ICB. A difference in OS was not observed in more socially vulnerable patients (SVI, not reached vs. 81.7 months), however, a survival advantage was evident with higher dietary fiber intake (not reached, 58.9 months). Conclusions: Increased social vulnerability was associated with a less favorable gut microbiome composition but not worse OS among melanoma and sarcoma patients treated with ICB. Consistent with prior findings, high dietary fiber intake emerged as a potentially modifiable pathway to improve outcomes in patients initiating ICB, particularly those with increased SVI.