Fiber-Boost: High-fiber diet with immunotherapy for advanced non-small cell lung cancer

Multicenter, Randomized, Controlled Trial to Study the Effects of a High-Fiber Dietary Intervention on ctDNA Clearance and the Microbial and Immunological Landscape in Patients With Advanced Non-Small Cell Lung Cancer Receiving PD-1/PD-L1-Targeted Monotherapy (Fiber-Boost)

This trial will test whether adding a high-fiber diet to first-line immunotherapy helps adults with advanced non-small cell lung cancer and how it changes the gut bacteria and immune response.

Quick facts

• Phase: Not applicable
• Study type: Interventional
• Enrollment: 42 (estimated)
• Ages: 18 Years and up
• Sex: All
• Sponsor: Cantonal Hospital of St. Gallen (Academic / other)
• Drugs / interventions: methotrexate, prednisone, immunotherapy
• Locations: 4 sites (Basel and 3 other locations)
• Trial ID: NCT07483112 on ClinicalTrials.gov

What this trial studies

Fiber-Boost randomizes 42 adults with advanced or recurrent NSCLC and PD-L1 ≥50% to receive either a supplement-based high-fiber diet or standard care while starting first-line PD-1/PD-L1 monotherapy for six weeks. The multicenter trial is conducted at four Swiss hospitals and collects stool for microbiome sequencing, blood for ctDNA quantification, and immune profiling to track biological effects. Participants are assigned to a test group (high-fiber intervention) or a control group with usual diet. The study seeks to link diet-driven changes in the gut microbiome to immune markers and potential treatment response.

Who should consider this trial

Good fit: Adults (≥18) with advanced or recurrent NSCLC, PD-L1 TPS ≥50%, no actionable driver mutations, ECOG 0–2, adequate organ function, and starting first-line PD-1/PD-L1 monotherapy are the intended participants.

Not a fit: Patients with targetable genetic alterations, those receiving combination chemo-immunotherapy, people unable to follow a high-fiber diet, or with poor organ function may be unlikely to benefit from this intervention.

Why it matters

Potential benefit: If successful, this approach could increase immunotherapy effectiveness and offer a low-risk, non-drug way to boost treatment response.

How similar studies have performed: Observational and early-phase studies link the gut microbiome and higher fiber intake to better immunotherapy outcomes, but randomized dietary interventions in NSCLC remain limited and exploratory.

Eligibility criteria

Inclusion Criteria:

* Age ≥18 years
* Written informed consent according to Swiss law and ICH/GCP regulations before inclusion and prior to any trial-specific procedures
* Histologically or cytologically confirmed NSCLC
* Advanced or recurrent NSCLC not amenable to curative treatment
* PD-L1 expression ≥50% (TPS) determined by an approved IHC test
* No actionable genetic alterations in genes such as EGFR, ALK, ROS1, HER2, BRAF, RET, MET, NTRK
* First-line palliative PD-1/PD-L1-targeted monotherapy at a 3-weekly schedule indicated per local investigator
* Willingness and ability to undergo study interventions
* ECOG performance status 0-2
* Adequate organ function:
* Hemoglobin ≥70 g/L, platelet count ≥50 G/L, granulocytes ≥1 G/L
* Bilirubin, ALT, AST ≤3 x ULN
* Glomerular filtration rate (Cockroft-Gault) ≥30 mL/min/1.73m²
* Measurable or evaluable disease per RECIST 1.1
* Patients with CNS metastases are eligible, provided there is no requirement for corticosteroids as therapy for CNS disease and no evidence of clinical progression
* Women with child-bearing potential use effective contraception (two independent methods), are not currently pregnant or lactating, and agree to not become pregnant during the trial treatment and during 3 months thereafter. A negative pregnancy test in either urine or blood is required for women with child-bearing potential before trial inclusion.
* Men who are not sterile agree to use contraceptive methods (condoms) or abstain from sexual intercourse during the trial treatment and 3 months thereafter.

Exclusion Criteria:

-History of malignancy, unless in remission for at least 3 years before inclusion with the exception of pT1-2 prostate cancer Gleason score \<6, adequately treated cervical carcinoma in situ or localized non-melanoma skin cancer

Adjuvant or additive systemic ICB treatment within 6 months prior to inclusion

* Systemic treatment with an antibiotic within 10 days of ICB treatment/HFD intervention start
* Concomitant immunosuppressive drugs including corticosteroids at a daily dose of ≥10mg prednisone equivalents, methotrexate, azathioprine, TNF-α inhibitors
* Concurrent treatment with other experimental drugs or other anticancer therapy
* Major surgical procedures within 14 days prior to inclusion as judged by the investigator
* Active autoimmune disease requiring systemic immunosuppressive treatment that is seen as contraindication for the use of PD-1/PD-L1-targeted monoclonal antibodies
* Uncontrolled diabetes mellitus
* Severe or uncontrolled cardiovascular disease
* Any other serious underlying medical, psychiatric, psychological, familial or geographical condition, which in the judgment of the investigator may interfere with the planned staging, treatment and follow-up, affect patient compliance or place the patient at high risk from treatment-related complications
* Had an allogeneic tissue/solid organ transplant
* Ongoing supplementation with OptiFibre® or another fiber supplement

Where this trial is running

Basel and 3 other locations

• Universitätsspital Basel — Basel, Switzerland (Not_yet_recruiting)
• Kantonsspital Graubünden — Chur, Switzerland (Not_yet_recruiting)
• HOCH Health Ostschweiz, Cantonal Hospital St.Gallen — Sankt Gallen, Switzerland (Recruiting)
• Kantonsspital Winterthur — Winterthur, Switzerland (Not_yet_recruiting)

Study contacts

• Study coordinator: Maximilian Boesch, Ph.D.

Conditions Non-Small Cell Carcinoma of Lung; non-small cell lung cancer; immunotherapy; high-fiber diet; microbiome