Sialyl-Thomsen-nouveau antigen (STn) (STn)

Sialyl-Thomsen-nouveau (STn) antigen is a truncated O-glycan disaccharide (Neu5Acα2-6GalNAcα1-Ser/Thr) that is aberrantly overexpressed on the surface of various epithelial cancers, including breast, gastric, and ovarian malignancies (Biomolecules, 2012; MDPI, 2023). It is a well-characterized tumor-associated carbohydrate antigen (TACA) that is typically absent or minimally expressed in normal adult tissues, providing a high degree of tumor specificity (NIH, 2017; Frontiers in Oncology, 2023). The expression of STn is primarily driven by the upregulation of the sialyltransferase ST6GalNAc1 or functional loss of the molecular chaperone COSMC, which prevents the normal elongation of O-glycan chains (Biomolecules, 2012; Frontiers in Oncology, 2023). Biologically, STn promotes tumor progression by enhancing cell migration, invasion, and metastasis, and it facilitates immune evasion by interacting with inhibitory receptors such as Siglec-15 and Siglec-9 on immune cells (Patsnap, 2024; Frontiers in Oncology, 2024). Therapeutic development has spanned several decades, beginning with the STn-KLH vaccine Theratope, which reached Phase III trials but failed to meet primary endpoints (Medscape, 2003; NIH, 2025). More recent efforts have focused on next-generation modalities, including glycopeptide-specific antibodies like gatipotuzumab and potent antibody-drug conjugates (ADCs) such as LM-338, which carry cytotoxic payloads like topoisomerase I inhibitors (NIH, 2025; AACR, 2026). Additionally, the STn-Siglec axis is being explored as a novel immune checkpoint for blockade (Frontiers in Oncology, 2024). Despite its potential, therapeutic success is challenged by the low immunogenicity of carbohydrate epitopes and the need for robust biomarkers, such as serum STn levels or immunohistochemical staining, to identify patients most likely to benefit from STn-targeted interventions (NIH, 2015; ResearchGate, 2026).

Other names

Sialyl-TnSTnCD175sNeu5Acα2-6GalNAcα1-Ser/ThrSialyl-Tn antigenSialyl-Thomsen-nouveau

Drugs targeting the Sialyl-Thomsen-nouveau (STn) antigen utilize several strategies: active immunotherapy (vaccines like Theratope) to induce endogenous humoral and cellular immune responses; passive immunotherapy (monoclonal antibodies like gatipotuzumab) to trigger antibody-dependent cellular cytotoxicity (ADCC) or block immunosuppressive signaling; and antibody-drug conjugates (ADCs like LM-338) to deliver cytotoxic payloads directly to STn-expressing tumor cells. Additionally, some agents target the STn-Siglec axis to reverse glycan-mediated immune suppression.