Re-analysis of two breast cancer cell lines, MCF-7 and MDA-MB-231, has shown multiple isomeric structures exposed by sequential mass spectrometry, MS n . Several released glycan compositions were re-evaluated, which indicated variations in polylactosamine and fucosylation structures. Probable isomer numbers, when considering both stereo and structural entities, are significant and the varying types are mentioned. The structural isomers of linkage position are most frequently considered, while stereo isomers are usually assumed from biosynthetic data. Evaluation of any new sample should be cautious and merits careful attention to empirical data. While isomers are usually considered a chromatographic problem (e.g., LCMS, IMMS) and most frequently considered a separations problem, such results will always be challenged by identification and documentation. MSn data provide a direct spatial solution that includes spectral data for characterization (mass and abundance) supported by a universal library match feature.