Intravital imaging of metastatic behavior through a mammary imaging window

The combination of a glass window placed on top of a mouse mammary gland with photoswitchable fluorescent protein labeling of implanted tumor cells allows tumor-cell tracking over multiple imaging sessions in orthotopic tumors. Results show the existence of two distinct microenvironments with different tumor-cell invasion and intravasation characteristics. We report a technique to evaluate the same tumor microenvironment over multiple intravital imaging sessions in living mice. We optically marked individual tumor cells expressing photoswitchable proteins in an orthotopic mammary carcinoma and followed them for extended periods through a mammary imaging window. We found that two distinct microenvironments in the same orthotopic mammary tumor affected differently the invasion and intravasation of tumor cells.