TNT induces phase-structured, non-linear gut ecosystem change, with Fx14 representing a reproducible mid-course bottleneck across ecological and resistance layers. Apparent improvements in relative metrics may reflect redistribution within a contracting community rather than true ecological recovery.
Main Session
Sep
28
PQA 03 - Digital Health Innovation and Informatics, Patient Safety & Quality, and Radiation and Cancer Biology
2458 - Phase-Structured Microbiome Reweighting with Dip-Rebound Diversity during TNT Reveals Fx14 as a Mid-Course Ecological Bottleneck
Presenter(s)
Kristof Gal, MD, PhD - University of Debrecen, Debrecen, Hajdú - Bihar
K. Gal, M. Barabás, P. Dávid, P. Fauszt, M. Paholcsek, E. Tolnai, J. Remenyik, and Á. Kovács; University of Debrecen, Debrecen, Hungary
Purpose/Objective(s):
To determine whether fraction-anchored longitudinal sampling can identify the temporal peak of gut ecosystem disruption during the EBRT component of total neoadjuvant therapy (TNT) in locally advanced rectal adenocarcinoma (RC), and to disentangle true ecological change from relative-abundance reweighting across microbiome and resistome layers.Materials/Methods:
Thirteen patients with locally advanced RC were prospectively followed during EBRT (50.4 Gy/28 fractions with concurrent fluoropyrimidine radiosensitisation) within TNT. Faecal samples were anchored to treatment fractions at baseline (Fx0), mid-treatment (Fx14), and end-treatment (Fx28). Non-RC individuals served as controls. Shotgun metagenomics was used to profile community biomass proxy, taxonomic structure, Shannon diversity, anaerobe configuration, oralisation index, biofilm-capable signal, and antimicrobial resistance features, including aggregated ARF-ARG burden, ARG class composition, dominant inferred carriers, and healthcare-associated infection (HAI)-linked fractions.Results:
Fx14 emerged as a microbiome–resistome inflection point. Compared with controls, community biomass proxy was consistently reduced and declined progressively over therapy, indicating community thinning. Shannon diversity displayed a V-shaped dip-and-rebound pattern, suggesting that diversity metrics were driven mainly by low-abundance taxa contributing little to total biomass. Bacterial reads remained dominant but dipped transiently at Fx14 with reciprocal increases in eukaryotic fractions, consistent with compositional redistribution rather than wholesale replacement. The ecosystem remained shifted away from a strictly anaerobe-leaning configuration throughout TNT, while canonical RC-associated taxa (including Fusobacterium nucleatum and Peptostreptococcus anaerobius) showed phase-structured trajectories and contracted by Fx28.
The oralisation index progressively normalised toward control-like values. In contrast, the biofilm-capable signal was elevated at baseline, peaked at Fx14, and attenuated by Fx28. Overall resistome burden varied modestly, but ARG class composition shifted, most notably with reduced tetracycline-class representation. Carrier-attributed ARF-ARG proportions remained broadly stable despite strong phase-structured changes in carrier abundance, with Bacteroides fragilis acting as a hub-like contributor. Although RC patients exhibited higher HAI-linked taxon fractions than controls, most aggregated ARF-ARG signal (~16.6%) remained attributable to non-HAI/background community members.
Conclusion: