Localization of Tamoxifen in Human Breast Tumor by MALDI Mass Spectrometry Imaging

Background: Tamoxifen is used in endocrine treatment of breast cancer to inhibit estrogen signaling. A set of strati‐ ed ER‐positive and ER‐negative tumor sections was subjected to manual deposition of tamoxifen solution in order to investigate its spatial distribution upon exposure to interaction within thin tissue sections.
Methods: The localization of tamoxifen in tumor sections was assessed by matrix assisted laser deposition/ioniza‐ tion mass spectrometry imaging. The images of extracted ion maps were analyzed for comparison of signal intensity distributions.
Results: The precursor ion of tamoxifen (m/z 372.233) displayed heterogeneous signal intensity distributions in his‐ tological compartments of tumor tissue sections. The levels of tamoxifen in tumor cells compared with stroma were higher in ER‐positive tissues, whereas ER‐negative tissue sections showed lower signal intensities in tumor cells.
Conclusions: The experimental model was successfully applied on frozen tumor samples allowing for di erentiation between ER groups based on distribution of tamoxifen.