To build comprehensive models of cellular states and interactions in normal and diseased tissue, genetic and proteomic information must be extracted with single-cell and spatial resolution. Here, we extended imaging mass cytometry to enable multiplexed detection of mRNA and proteins in tissues. Three mRNA target species were detected by RNAscope-based metal in situ hybridization with simultaneous antibody detection of 16 proteins. Analysis of 70 breast cancer samples showed that HER2 and CK19 mRNA and protein levels are moderately correlated on the single-cell level, but that only HER2, and not CK19, has strong mRNA-to-protein correlation on the cell population level. The chemoattractant CXCL10 was expressed in stromal cell clusters, and the frequency of CXCL10-expressing cells correlated with T cell presence. Our flexible and expandable method will allow an increase in the information content retrieved from patient samples for biomedical purposes, enable detailed studies of tumor biology, and serve as a tool to bridge comprehensive genomic and proteomic tissue analysis. Display omitted •Imaging mass cytometry enables multiplexed RNA and protein detection in situ•mRNA measurement in IMC enables detection of as little as 6–14 mRNA copies per cell•Among patients, mRNA-to-protein ratios vary for CK19 but not for HER2•CXCL10-expressing cells form patches and are associated with T cell abundance Here, we extend imaging mass cytometry to enable multiplexed detection of mRNA and protein in single cells in tissue sections. We show rigorous validation of the method and apply it to 70 samples from breast cancer patients. We investigate single-cell and population-based RNA-to-protein correlations in tissue and identify rare chemokine-expressing cells in the stroma that are associated with T cell abundance.