OBJECTIVES : This study evaluated the cost-effectiveness of adding a gut microbiome test (GMT) to PD-L1 testing to guide treatment choice between immunotherapy and chemotherapy options in the care of patients with metastatic or unresectable melanoma.

METHODS : This study applied a decision tree model to study the cost-effectiveness of adding a gut microbiome test (GMT) to routine PD-L1 testing to guide treatment decisions for patients with metastatic or unresectable. Treatment options included immunotherapy or chemotherapy protocol. The analysis was conducted from the public perspective; the majority of patients were Medicare beneficiaries. The model’s time horizon was 32 weeks or 16 weeks depending on whether patients’ first-line treatment fails. Costs were calculated in US Dollars (USD, $) and adjusted for inflation to 2019 USD. Quality-adjusted life years (QALYs) were used to measure effectiveness. Both univariate and probabilistic sensitivity analyses were used to assess the reliability of the deterministic results and examine the uncertainties in the model. Microsoft Excel (version 16.29.1) was used for modeling.

RESULTS : Patients accrued 1.11 more QALYs and cost $32,981 more compared to standard of care of using PD-L1 testing alone. The incremental cost effectiveness ratio of GMT strategy was $75,229 per QALY under base-case assumptions. The 95% credible interval for the ICER was $42,739/QALY to $99,176/QALY. 75.4% of the 10,000-iteration Monte-Carlo probabilistic sensitivity analysis simulations yielded cost-effective results under a $75,000/QALY willingness-to-pay threshold.

CONCLUSIONS : Adding microbiome testing to the routine use of using PD-L1 testing is a cost-effective strategy for guiding treatment of metastatic or unresectable melanoma with willingness-to-pay threshold of $100,000 or above. The addition of GMT may provide economic and clinical value in the care treatment paradigm of metastatic or unresectable melanoma.