A multiresolution investigation combining single-cell RNA sequencing, high-definition spatial transcriptomics, and experimental validation models has revealed that recurrent hypopharyngeal squamous cell carcinoma represents a fundamentally reassembled tumor ecosystem defined by distinct post-transcriptional, stromal, and immunosuppressive programs. Hypopharyngeal squamous cell carcinoma is an exceptionally lethal malignancy that constitutes less than five percent of all head and neck squamous cell carcinomas, carrying an unfavorable five-year overall survival rate of thirty to forty percent. A major determinant of mortality in this disease is its pronounced tendency to recur rapidly following initial treatment, with approximately half of all diagnosed patients experiencing tumor recurrence within twelve months. Because clinical options for curative salvage therapy in recurrent disease remain severely restricted, researchers have sought to delineate the cellular heterogeneity and regulatory networks that distinguish post-treatment recurrent lesions from treatment-naive primary tumors. By profiling human tissue specimens alongside cell-line and xenograft systems, investigators demonstrated that recurrent tumors do not merely represent expanding residual primary cells, but instead undergo extensive phenotypic and microenvironmental reprogramming characterized by enhanced stemness, fibronectin-dependent stromal interactions, and marked immune evasion.
To capture the cellular composition of primary and recurrent disease, investigators collected surgical tissues from six treatment-naive primary patients and three patients who experienced cancer recurrence following chemotherapy and radiation therapy at the First Affiliated Hospital of Sun Yat-sen University. The resulting clinical collection comprised six primary tumor specimens, two matched adjacent mucosal tissues, and three recurrent tumor specimens. Using droplet-based single-cell RNA sequencing libraries evaluated on high-throughput sequencing systems, the researchers profiled eighty-nine thousand four hundred and seventy-six individual cellular transcriptomes after applying rigorous quality-control thresholds and batch correction algorithms. Across the integrated dataset, which encompassed forty-four thousand and nineteen cells from primary lesions, sixteen thousand seven hundred and ninety cells from adjacent mucosal tissues, and twenty-eight thousand six hundred and sixty-seven cells from recurrent lesions, eight major lineages were identified through canonical marker expression. These populations included thirty-six thousand nine hundred and sixty-eight epithelial cells, eighteen thousand two hundred and forty-six T and natural killer T cells, nine thousand five hundred and fifty-nine neutrophils, seven thousand seven hundred and ninety-nine fibroblasts, seven thousand six hundred and thirteen myeloid cells, five thousand five hundred and ninety-seven B cells, two thousand six hundred and sixty-five endothelial cells, and one thousand and twenty-nine mast cells.
Chromosomal copy number variation profiling resolved the malignant epithelial compartment from normal non-malignant epithelial lineages, revealing that recurrent malignant epithelial cells exhibited significantly elevated genomic instability scores compared with their primary counterparts. Differential gene expression and pathway enrichment analyses demonstrated that recurrent malignant cells displayed an upregulation of stemness-associated markers, including CD44, KLF4, IQGAP1, YAP1, and ALCAM, accompanied by the selective enrichment of epithelial-mesenchymal transition and developmental signaling pathways. Simultaneously, recurrent cancer cells upregulated immunosuppressive mediators such as NECTIN2, MIF, GPNMB, CXCL1, and CD59, while markedly downregulating major histocompatibility complex class I antigen-presenting genes including HLA-A, HLA-B, and HLA-C. These recurrent malignant populations also exhibited elevated expression of the anti-phagocytic checkpoint markers CD47 and CD24, which engage SIRP-alpha and Siglec-10 receptors on macrophages. In striking contrast, primary malignant epithelial cells were predominantly characterized by high transcriptional activity in proliferation and cell-cycle pathways, including E2F targets, MYC targets, and the G2/M checkpoint, alongside heightened oxidative phosphorylation and fatty acid metabolism signatures.
Transcription factor regulon analysis pinpointed aberrant transcriptional activation of SMAD3 within recurrent malignant epithelial cells, aligning with an observed enrichment of transforming growth factor beta signaling. Concurrently, differential expression testing identified the selective upregulation of IGF2BP2, a recognized N6-methyladenosine RNA reader protein, within recurrent malignant cells. Subsequent biochemical investigations in FaDu human hypopharyngeal cancer cells confirmed that IGF2BP2 directly binds to SMAD3 transcripts through methylated RNA motifs, protecting the transcript from rapid degradation. Following transcriptional arrest mediated by actinomycin D, stable lentiviral overexpression of IGF2BP2 substantially delayed SMAD3 transcript decay over six hours compared with control cells. Functional assays demonstrated that elevated IGF2BP2 expression amplified FaDu cell migration, Matrigel invasion, and tumorsphere generation while shifting epithelial and mesenchymal protein levels. These malignant phenotypes were substantially reversed when cells were exposed to the selective SMAD3 phosphorylation inhibitor SIS3, indicating that the phenotypic plasticity conferred by IGF2BP2 requires functional SMAD3 activation.
The functional relevance of the IGF2BP2-SMAD3 axis was subsequently verified in vivo through cell line-derived xenograft models established in immunocompromised nude mice. Animals bearing subcutaneous tumors generated from IGF2BP2-overexpressing FaDu cells developed significantly larger tumor burdens over twenty-seven days than controls harboring empty vectors. Daily administration of the SMAD3 phosphorylation inhibitor SIS3 markedly suppressed this accelerated tumor growth, yielding significantly smaller tumor volumes. Immunohistochemical staining confirmed that tumors derived from IGF2BP2-overexpressing cells displayed elevated levels of phosphorylated SMAD3, CD44, and vimentin without significant alterations in E-cadherin expression, whereas pharmacological inhibition with SIS3 reversed the expression of these marker proteins. Furthermore, methylated RNA immunoprecipitation quantitative PCR demonstrated that treating cells with CWI1-2, a small-molecule antagonist that blocks IGF2BP2 from binding N6-methyladenosine-modified targets, substantially diminished the methylation enrichment of SMAD3 transcripts. These experimental findings verify that post-transcriptional transcript stabilization mediated by IGF2BP2 sustains downstream transforming growth factor beta signaling to reinforce cancer stem-cell properties and invasive capacity in hypopharyngeal carcinoma.
Intercellular communication modeling revealed that recurrent malignant cells engaged in significantly denser signaling cross-talk with stromal fibroblasts than primary malignant cells. High-resolution clustering of the fibroblast compartment identified six distinct functional subsets: extracellular matrix cancer-associated fibroblasts, developmental cancer-associated fibroblasts, antigen-presenting fibroblasts, myofibroblastic fibroblasts, elastic fibroblasts, and pericytes. Notably, developmental fibroblasts expressing stemness-associated regulators like SCRG1 and SOX9 were specifically enriched in recurrent specimens. High-definition spatial transcriptomics using contiguous two-micrometer features binned at sixteen micrometers revealed that developmental, extracellular matrix, and myofibroblastic fibroblasts formed structured peritumoral niches immediately adjacent to cancer nests along the invasive margins of recurrent tumors. Within these spatial niches, signaling interactions between fibroblasts and recurrent cancer cells were heavily driven by fibronectin 1, which interacted with malignant cell receptors including syndecan-1, syndecan-4, and CD44. In primary tumors, by comparison, stromal-epithelial communication probabilities involving fibronectin 1 and extracellular matrix components remained substantially lower.
To evaluate whether targeting fibronectin 1 signaling could disrupt tumor growth in vivo, researchers established human recurrent hypopharyngeal cancer patient-derived xenografts in mice and administered either the targeted peptide inhibitor RGDS or an inactive control peptide, RGES, three times weekly for three weeks. Treatment with the RGDS inhibitor significantly restricted xenograft expansion and reduced terminal tumor volumes compared with control peptide administration. Histological and immunohistochemical analyses demonstrated that blocking fibronectin interactions led to substantial reductions in tumor cell proliferation and stemness markers, specifically diminishing Ki-67, CD44, and vimentin expression while maintaining cell adhesion structures. These preclinical animal data confirmed that extrinsic fibronectin signaling from neighboring cancer-associated fibroblasts acts as an essential external driver that sustains the aggressive phenotype of recurrent hypopharyngeal tumor cells. The convergence of stromal fibronectin signaling with tumor-intrinsic IGF2BP2-mediated programs highlights a cooperative network operating across cellular compartments to reinforce malignant behavior following initial treatment failure.
Characterization of the immune compartment demonstrated profound functional divergence in cytotoxic T-cell populations between primary and recurrent microenvironments. Subclustering of T and natural killer T cells defined four CD8-positive subsets, including interferon-stimulated CD8-positive T cells, exhausted CD8-positive T cells, and two cytotoxic effector populations. While primary tumors retained substantial representation of cytotoxic effector subsets expressing granzyme B, granzyme H, granzyme M, and NKG7, recurrent tumors exhibited a significant expansion of exhausted CD8-positive T cells displaying elevated expression of inhibitory receptors and transcriptional drivers including TOX, FOXP1, NR4A3, CBLB, and ICOS. Unsupervised pseudotime trajectory analysis reconstructed a progressive transition from early interferon-responsive phenotypes through cytotoxic stages to late-stage exhaustion. Strikingly, CD8-positive T cells from primary tumors populated early and intermediate cytotoxic stages, whereas cells from recurrent tumors mapped almost exclusively to terminal exhaustion. Notably, rather than relying solely on classical PD-1 dominance, recurrent cytotoxic T cells exhibited premature, aberrant upregulation of CTLA4, an observation corroborated by multiplex immunohistochemistry showing elevated frequencies of CD8-positive CTLA4-positive infiltrating lymphocytes in recurrent human tissues.
In parallel with cytotoxic lymphocyte dysfunction, the myeloid lineage within recurrent hypopharyngeal tumors underwent comprehensive remodeling toward an immunosuppressive state. Unsupervised myeloid clustering resolved nine distinct populations, including monocytes, four tumor-associated macrophage subsets, and four dendritic cell subsets. Among these, macrophages expressing SPP1 were markedly enriched in recurrent lesions and displayed high angiogenic gene scores alongside reduced phagocytosis-related expression. Although primary macrophages displayed a balance of inflammatory characteristics, comparative scoring demonstrated that macrophages in recurrent tumors underwent a significant shift toward an immunosuppressive M2-like polarization state, accompanied by a sharp decline in M1-associated proinflammatory scores. Furthermore, the recurrent tumor microenvironment contained an expanded population of mature, tolerogenic LAMP3-positive dendritic cells expressing migration and immunosuppressive markers such as CCR7, CD274, and IDO1. Quantitative pathway scoring confirmed that dendritic cells isolated from recurrent tumors suffered a statistically significant reduction in antigen-presentation capacity compared with their counterparts in primary disease, thereby establishing a myeloid environment that impairs effective adaptive immune responses.
Despite providing a detailed multicellular atlas of recurrence mechanisms, the study design presents several recognized limitations that constrain broad biological generalization. Crucially, the analyzed recurrent surgical specimens were not obtained from the identical patients who contributed the treatment-naive primary tumors, precluding direct tracking of longitudinal clonal evolution within individual hosts. Additionally, the overall clinical sample cohort was relatively modest, comprising nine total cancer patients, which necessitates confirmation in larger patient registries to capture the full spectrum of inter-patient tumor heterogeneity. In vitro functional experiments were largely restricted to the FaDu cell model because robust alternative human hypopharyngeal cancer cell lines are scarce, and mechanistic testing relied primarily on pharmacological inhibitors rather than genetic knockout strategies. Furthermore, while the RGDS peptide successfully suppressed xenograft growth in patient-derived models, it broadly targets conserved integrin-binding motifs that are shared with alternative ligands such as vitronectin and osteopontin. Consequently, prospective clinical trials and genetic perturbation studies will be essential to validate whether dual immune checkpoint blockade or targeted disruption of the IGF2BP2-fibronectin network can overcome treatment resistance in patients with recurrent hypopharyngeal malignancy.
Subject of Research: Single-cell and spatial transcriptomic profiling of primary and recurrent hypopharyngeal squamous cell carcinoma microenvironments
Article Title: Single-cell and spatial transcriptomic analysis reveal distinct tumor microenvironment signatures in primary and recurrent hypopharyngeal squamous cell carcinoma
Article References: Cai, Z., Zhang, J., Ding, Y., Xu, Z., Liu, Z., Qiang, Z., Lu, Z., Chen, L., Wen, W., & Lei, W. (2026). Single-cell and spatial transcriptomic analysis reveal distinct tumor microenvironment signatures in primary and recurrent hypopharyngeal squamous cell carcinoma. Cellular & Molecular Biology Letters, 31(1), Article 146. https://doi.org/10.1186/s11658-026-00991-z
Image Credits: AI Generated
DOI: 10.1186/s11658-026-00991-z
Keywords: hypopharyngeal squamous cell carcinoma, single-cell RNA sequencing, spatial transcriptomics, tumor microenvironment, IGF2BP2, SMAD3, m6A methylation, cancer-associated fibroblasts, fibronectin 1, CD8+ T-cell exhaustion, CTLA4, SPP1+ macrophages, LAMP3+ dendritic cells, epithelial-mesenchymal transition, patient-derived xenografts, FaDu cells
Tags: Cancer-associated fibroblastsCD8+ T cell exhaustionCTLA4Epithelial-mesenchymal transitionFaDu cellsfibronectin 1hypopharyngeal squamous cell carcinomaIGF2BP2LAMP3+ dendritic cellsm6A methylationpatient-derived xenograftssingle-cell RNA sequencingSMAD3Spatial transcriptomicsSPP1 macrophagestumor microenvironment
