CD44 is associated with papillary thyroid carcinoma metastasis via potential modulation of the immunosuppressive tumor microenvironment.

To investigate the role of CD44 in papillary thyroid carcinoma (PTC) lymph node metastasis and its connotation with Treg-mediated immunosuppression through TGF-β and IL-10 signaling. Eighty-two benign thyroid nodule patients were compared with 122 PTC patients. Differentially expressed proteins (DEPs) were identified in both tissue and serum. CD44 expression was validated by ELISA, IHC and flow cytometry. The proportion of Treg and cytokines were analyzed in parallel. The tumor microenvironment architecture was examined using 3D tissue clearing and whole-mount imaging. The functional role of CD44 was further explored using TPC-1 human PTC cell line through gain-of-function and loss-of-function assays in vitro. Proteomic analysis identified 34 tissue and 17 serum DEPs involved in metastasis. CD44 levels in serum were significantly higher in PTC patients than in controls (345.45 ± 44.88 pg/mL vs. 73.33 ± 25.64 pg/mL, P < 0.001). Furthermore, CD44 expression in the serum of CLNM patients was further elevated (782.01 ± 168.38 pg/mL vs. 248.77 ± 55.33 pg/mL, P < 0.001). Multivariate analysis identified CD44 as an independent risk factor for PTC (OR = 5.271, 95% CI: 1.741 ~ 15.959) and CLNM (OR = 3.995, 95% CI: 1.298 ~ 12.298). CD44 levels showed positive correlations with increased TGF-β, IL-10 levels, and Treg frequency. CD44 levels were connected with amplified TGF-β, IL-10, and Treg frequency. IHC and 3D imaging also demonstrated colocalization of CD44⁺ tumor cells and Tregs in H&E sections and whole-mount. Importantly, CD44 knockdown suppressed, while CD44 overexpression enhanced, TPC-1 cell proliferation in vitro, suggesting a direct role of CD44 in promoting tumor cell growth. Our data suggest that CD44 may contribute to PTC metastasis by modulating the immunosuppressive microenvironment through TGF-β/IL-10 mediated Treg accumulation and by directly driving tumor cell proliferation. These findings highlight a potential pathogenic role of CD44 in PTC progression. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10238-026-02101-x.