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.

Social vulnerability index was inversely correlated with dietary fiber intake in patients with melanoma or sarcoma treated with immune checkpoint blockade.

• 153 patients with melanoma or sarcoma treated with immune checkpoint blockade (ICB) were prospectively followed
• Median SVI percentile was 0.4 (IQR, 0.2–0.7)
• Median dietary fiber intake was 17 (IQR, 15–20) g/day
• Inverse correlation between SVI percentile and dietary fiber intake: r = -0.18, p = .0398

Increased social vulnerability was associated with less favorable gut microbiome community composition and lower alpha-diversity.

• Gut microbiome analyses revealed community and compositional differences by SVI
• SVI was inversely associated with α-diversity
• SVI was inversely associated with relative abundance of favorable bacteria such as Bifidobacterium longum (p < .001)
• Dietary fiber intake showed positive associations with the same microbial markers, contrasting the inverse associations seen with SVI

Higher dietary fiber intake was associated with measurable response to immune checkpoint blockade.

• Increased dietary fiber intake was associated with measurable response to ICB
• This finding was observed regardless of gut microbiome dysbiosis and social vulnerability
• The association is described as consistent with prior findings in the literature

Higher dietary fiber intake was associated with a survival advantage, whereas increased social vulnerability was not associated with worse overall survival.

• Patients with higher dietary fiber intake had overall survival of 'not reached' versus 58.9 months for those with lower fiber intake
• In more socially vulnerable patients, overall survival was 'not reached' versus 81.7 months, and no statistically significant difference in OS was observed by SVI
• Increased social vulnerability was associated with a less favorable gut microbiome composition but not worse OS among melanoma and sarcoma patients treated with ICB

High dietary fiber intake was identified as a potentially modifiable pathway to improve outcomes in patients initiating immune checkpoint blockade, particularly those with increased social vulnerability.

• The study hypothesized that increasing social vulnerability would be associated with insufficient dietary fiber intake and negatively associated with microbiome composition and clinical outcomes
• Dietary fiber emerged as a modifiable factor even among patients with increased SVI
• The findings suggest dietary fiber intervention may be particularly relevant for socially vulnerable patients initiating ICB