Stromal Cells as Targets for Image-Guided Surgery of Breast Cancer

The distinction between malignant and normal tissue is not always evident. Image-guided surgery (IGS) is a technique using near-infrared fluorescent (NIRF) probes to visualize tumor tissue during the operation. NIRF light offers a relatively deep tissue penetration in combination with low tissue auto-fluorescence. NIRF light is invisible for the human eye and does not interfere with the surgeons view. Special camera systems and software visualize the NIRF signal on a monitor. The ‘contrast agents’ or probes consist generally of a NIRF dye conjugated to an antibody directed against a target protein. Most of the target proteins presently under evaluation for IGS are cell membrane proteins, over-expressed on malignant, epithelial-derived cells. Next to these malignant cells, many cancers consist for a substantial part of stromal cells and extracellular matrix. Stromal cells are a physiological reaction of the body and the expression of their cell membrane protein repertoire will not directly be influenced by genetic alterations, like for malignant cells.

To determine whether stromal cells could be an alternative target for IGS of breast cancer, we have evaluated the presence of stromal cells in lobular and ductal tumors using immunohistochemistry on sequential sections from paraffin embedded tissues. Lobular tumors consisted for 26-72% of stromal tissue and lobular tumors slightly less (26-43%). Antibodies against pan-cytokeratin, vimentin, CD31, CD105, CD45, CD68, CD163, and α-SMA identified the major stromal cell types: endothelial cells, from which approximately 50% stained with CD31 as well as CD105, indicating a neo-angiogenic state; immune cells, from which the majority appeared to be type 1 macrophages; and fibroblasts with a substantial part of the activated α-SMA expressing phenotype. Our results underline the potential of stroma cells, as target for IGS.