Mass spectrometry imaging (MSI) was used to investigate different tumors regions from five head and neck squamous cell carcinoma (HNSCC) xenograft samples of tumor model CAL33. Specifically, the authors investigated if measurements could be attributed to tumor hypoxia. Hypoxic regions were defined using consecutive tissue slices which were stained with anti-pimonidazole polyclonal antibody. M/z values which were associated to hypoxic regions were converted to masses and mapped with masses from LC-MS/MS experiment. LC-MS/MS experiment was carried out on three different HNSCC xenografts samples from the same tumor model (CAL33). For details see: https://doi.org/10.21203/rs.3.rs-3755587/v1