An exploratory analysis of the phase 2 PROMIT trial found that gut microbiome TOPOSCORE classifications did not predict outcomes in patients with primary resistant metastatic melanoma receiving chemotherapy and immunotherapy re-induction. The finding suggests the proposed microbiome stratifier may not generalize to the specific re-induction context examined in the trial. The result matters for precision oncology biomarker development because it emphasizes the need for model revalidation across treatment sequences and patient subsets before clinical adoption.