MS imaging allows profiling and imaging of compounds directly from tumor tissue, tissue microarrays and tissue-engineered models of tumors. Methodologies for the quantitative analysis of localized/colocalized ion signals from a single cancer cell would be a major advance. Alternative methods of generating ions to matrix-assisted laser desorption ionization are increasingly employed. Desorption electrospray ionization has been used for the intraoperative diagnosis of human brain tumors and secondary ion MS imaging with cluster primary ion sources has been used for high spatial resolution imaging tumor sections. Extensive validation of the technique for the analysis of disease biomarkers is required, if imaging MS is to have a future role in the clinic.