Figure 1

Phenotypic changes of breast cancer cells during dissemination and metastasis. Epithelial tumor cells that originated from a primary tumor might transform into more aggressive phenotypes and disseminate into the blood or lymph circulation. Due to this altered phenotype, which is frequently associated with epithelial-mesenchymal transition (EMT), their detection and identification in blood of cancer patients is significantly hampered. After surviving in the blood stream and homing to a secondary organ, tumor cells may undergo mesenchymal-epithelial transition (MET) and assimilate into the new environment of their secondary site (for example, bone marrow). This process will lead to the establishment of occult micrometastases that may eventually grow out to overt metastases detectable with current imaging methods.