Longitudinal Changes in Urinary ExoQuick-TC-Enriched Fraction-Derived Tryptic Peptides Following Thyroidectomy in Well-Differentiated Thyroid Cancer: The t-UXEDO Study

Background: Differentiated thyroid cancer generally has a favorable prognosis; however, postoperative surveillance remains important because persistent or recurrent disease may occur. Urinary fractions enriched by extracellular-vesicle precipitation methods represent a potential noninvasive source of proteomic biomarkers, although these preparations may contain co-isolated non-vesicular proteins. We investigated longitudinal changes in tryptic surrogate peptides measured from an ExoQuick-TC-enriched urinary fraction following thyroidectomy in patients with well-differentiated thyroid cancer. Methods: This prospective single-center exploratory study included 21 patients with papillary or follicular thyroid carcinoma. The clinical study was initiated in 2017, following earlier analytical development. Urine samples were collected before thyroidectomy and at five postoperative time points through 24 months. Predefined tryptic surrogate peptides were quantified using targeted liquid chromatography–multiple reaction monitoring tandem mass spectrometry (LC-MRM/MS). Available preoperative and 1-week postoperative paired urinary peptide measurements were reanalyzed using two-sided exact Wilcoxon signed-rank tests, with exploratory Benjamini–Hochberg false-discovery-rate (BH-FDR) adjustment. Results: Twenty-one patients were included in the final analysis; the median age was 49 years, and 18 (85.7%) were women. No clinical recurrence was observed during 24 months of follow-up. Several urinary fraction-derived tryptic surrogate peptides exhibited variable postoperative patterns. Among patients with lymph-node metastasis, Keratin-19 showed a nominal early postoperative decrease (exact p = 0.0156). In the I-131-treated subgroup, Keratin-19 also demonstrated a nominal postoperative association (exact p = 0.0176), whereas Calprotectin A8 did not reach nominal statistical significance (exact p = 0.0676). None of these associations remained statistically significant after BH-FDR adjustment within the 12 urinary peptide targets available for exact reanalysis. Conclusions: Longitudinal targeted proteomic measurements from an ExoQuick-TC-enriched urinary fraction demonstrated exploratory postoperative changes in selected tryptic surrogate peptides. These observations do not establish exosome-specific biomarker performance, disease specificity, or recurrence-prediction utility. Larger prospective studies with standardized analytical procedures and independent validation are warranted.