Proteomic characterization of microdissected epithelium, tumor cells, and stroma from breast tissues

Tissue of the breast is heterogeneous, consisting of a variety of cell types and connective tissue. This heterogeneity is also present in breast tumors and will complicate proteomic analysis, as it is not always clear whether a signal originates from the stromal environment, from normal epithelial or tumor cells. Here we microdissected a variety of cell types and stroma from benign and malignant breast tissues. We compared proteomic differences between these tissues, both from cells of epithelial origin and the stromal environment. Differences in protein abundances corresponded with several hallmarks of cancer, including loss of cell adhesion, transformation to a migratory phenotype, and enhanced energy metabolism. Furthermore, despite enriching for (tumor) epithelial cells, many changes to the extracellular matrix were detected in microdissected cells of epithelial origin. The stromal compartment was heterogeneous and richer in the number of fibroblast and immune cells in malignant sections, compared to benign tissue sections. Although this heterogeneity complicated detection of differentially abundant proteins, several markers were exclusively detected in stroma. However, as heterogeneity in the stroma is more difficult to be reduced through microdissection, comparative analysis was most informative in microdissected cells of epithelial origin, and provided a relatively complete picture of malignant transformations.