Introduction: For decades, the role of glycans and glycoproteins in the progression of breast cancer and other cancers have been evaluated. Through extensive studies focused on elucidating the biological functions of glycosylation, researchers have been able to implicate alterations in these functions to tumor formation and metastasis. Areas covered: In this review, we summarize how changes in glycosylation are associated with tumorigenesis, with emphasis on breast cancers. An overview of the changes in N-linked and O-linked glycans associated with breast cancer tumors and biofluids are described. Recent advances in glycomics are emphasized in the context of continuing to decipher the glycosylation changes associated with breast cancer progression. Expert opinion: While changes in glycosylation have been studied in breast cancer for many years, the clinical relevance of these studies has been limited. This reflects the inherent biological and clinical heterogeneity of breast cancers. Glycomics analysis lags behind the advances in genomics and proteomics, but new approaches are emerging. A summary of known glycosylation changes associated with breast cancer is necessary to implement new findings in the context of clinical outcomes and therapeutic strategies. A better understanding of the dynamics of tumor and immune glycosylation is critical to improving emerging immunotherapeutic treatments.

(1) Glycoproteins account for ~80% of proteins located at the cell surface and in the extracellular matrix. A growing body of evidence indicates that α-L-fucose protein modifications contribute to breast cancer progression and metastatic disease. (2) Using a combination of techniques, including matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS) based in cell and on tissue imaging and glycan sequencing using exoglycosidase analysis coupled to hydrophilic interaction ultra-high performance liquid chromatography (HILIC UPLC), we establish that a core-fucosylated tetra-antennary glycan containing a single N-acetyllactosamine (F(6)A4G4Lac1) is associated with poor clinical outcomes in breast cancer, including lymph node metastasis, recurrent disease, and reduced survival. (3) This study is the first to identify a single N-glycan, F(6)A4G4Lac1, as having a correlation with poor clinical outcomes in breast cancer.

Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer lacking targeted therapies. Although aberrant N-glycosylation is a hallmark of malignancy, the specific roles of core-fucosylated (CF) and outer arm–fucosylated (OAF) N-glycans in TNBC progression and patient survival remain underexplored. This study utilized multiplexed glycomics by matrix-assisted laser desorption/ionization imaging mass spectrometry to spatially profile 348 N-glycans in 59 TNBC tumors with clinical characteristics including survival data. Spatial analysis revealed distinct localization patterns of CF and OAF isomers within tumor microenvironments. Strikingly, OAF glycans, but not CF, were strongly associated with tumor stage, with expression increasing from stage I to III and then declining in stage IV. Furthermore, 68 N-glycans were significantly associated with survival outcomes; 36 (52%) of these were OAF-modified, including polylactosamine structures previously linked to metastasis in breast cancer. High expression of OAF polylactosamines correlated with poor prognosis and was detectable in early-stage TNBC tumors, underscoring their potential as prognostic biomarkers. Implications: These findings demonstrate that OAF N-glycans are dynamic, structure-specific markers of TNBC progression and survival, and their early detection and strong prognostic value highlight potential utility in patient stratification and personalized therapy.