Single-cell and bulk transcriptomic analyses identify B-cell senescence-associated biomarkers in papillary thyroid carcinoma

<h4>Background</h4>Papillary thyroid carcinoma (PTC) exhibits marked clinical heterogeneity that cannot be fully explained by tumor-intrinsic alterations alone. Emerging evidence suggests that immune cell senescence, particularly within B-cell compartments, may critically reshape the tumor immune microenvironment (TIME) and influence disease progression. However, the molecular determinants and clinical relevance of B-cell senescence in PTC remain poorly defined. The aim of this study was to identify B-cell senescence-related biomarkers and their clinical relevance in PTC.<h4>Methods</h4>We integrated single-cell RNA sequencing (scRNA-seq) and bulk transcriptomic data from public cohorts to systematically characterize senescence-associated transcriptional programs in tumor-infiltrating B cells. Differential expression analyses, survival modeling, and machine-learning-based risk stratification were performed to identify prognostic biomarkers. Immune infiltration, mutational landscapes, drug sensitivity profiles, intercellular communication networks, and B-cell differentiation trajectories were interrogated. Key findings were further validated in clinical PTC specimens via quantitative reverse transcription polymerase chain reaction (qRT-PCR).<h4>Results</h4>Single-cell analysis resolved eight major cell populations within PTC and revealed profound transcriptional remodeling of B cells in the tumor microenvironment (TME). Integrative filtering identified four senescence-associated biomarkers-<i>FOS</i>, <i>HSPA5</i>, <i>EGR2</i>, and <i>ABI3</i>-that collectively stratified patients into high- (HRG) and low-risk groups (LRG) with significantly different progression-free outcomes. The high-risk group exhibited distinct immune infiltration patterns, increased BRAF mutation burden, and differential sensitivity to multiple targeted agents. Pathway analyses linked these biomarkers to oncogenic signaling axes, including TGF-β, Wnt, and calcium signaling. Cell-cell communication analysis uncovered enhanced crosstalk between B cells, natural killer (NK) cells, and myeloid populations, while pseudotime analysis delineated dynamic, stage-specific expression of senescence markers along B-cell differentiation trajectories. Experimental validation confirmed aberrant expression of these biomarkers in clinical PTC tissues.<h4>Conclusions</h4>Our study identifies a strong association between B-cell senescence signatures and disease progression, and nominates <i>FOS</i>, <i>HSPA5</i>, <i>EGR2</i>, and <i>ABI3</i> as potential biomarkers whose mechanistic roles warrant further functional investigation. The identified biomarker axis provides a robust prognostic framework and highlights potential immunotherapeutic and pharmacologic vulnerabilities, offering new avenues for precision management of PTC.