Trimethylamine N-oxide as a potential biomarker for predicting axillary lymph node metastasis in breast cancer: a retrospective study

Axillary lymph node (ALN) metastasis is a critical prognostic factor in breast cancer, but current assessment methods have limitations. Trimethylamine N-oxide (TMAO), a gut microbiota-derived metabolite, has been implicated in tumor progression, though its role in breast cancer remains unclear. This retrospective study analyzed TMAO levels in breast tissue from benign breast nodules (BBN, n = 10), ductal carcinoma in situ (DCIS, n = 10), and invasive ductal carcinoma (IDC, n = 10). A cohort of 97 treatment-naive IDC patients (26 ALN + , 71 ALN −) was further evaluated. TMAO concentrations were quantified via ELISA, and associations with clinicopathological features were assessed using logistic regression and ROC analysis. TMAO levels were significantly higher in IDC (113.9 ± 16.36 ng/g) than in DCIS (82.29 ± 13.84 ng/g, p < 0.01) or BBN (76.09 ± 10.32 ng/g, p < 0.001). ALN + patients exhibited elevated TMAO (210.92 ± 82.09 ng/g) versus ALN − (122.99 ± 48.23 ng/g, p < 0.001). Multivariable analysis identified TMAO (OR = 1.022, 95% CI: 1.009–1.031), T-stage (T1 vs T2, OR = 1.201, 95% CI: 1.019–2.169), and axillary ultrasound positivity (OR = 6.993, 95% CI: 1.099–45.455) as independent predictors. A combined model (TMAO + T-stage + ultrasound) improved predictive accuracy (AUC = 0.915; 95% CI: 0.838–0.992). TMAO levels correlate with breast cancer progression and ALN metastasis, demonstrating potential as a biomarker. Further studies are needed to validate its clinical utility and mechanistic role.