Figure 1.

Possible fates of tumor cells detached from primary tumor.

Notes: Tumor cells disseminate at a secondary site and are subject to one of three possible fates: the tumor cells can proliferate aggressively, resulting in early metastasis; undergo apoptosis and die; or remain dormant. Two hypothetical models of tumor dormancy in breast cancer can occur: (1) in the single-cell dormancy model (left), cells derived from primary tumor remain quiescent in a state of G0–1 mitotic arrest at a secondary site and may be reactivated by genetic changes or by an altered microenvironment. (2) in the micrometastatic dormancy model (right), tumor cells proliferate and continue to form micrometastases at secondary homing sites. The micrometastases have a balanced state of proliferation and apoptosis; their growth is regulated by angiogenic and immunological factors within the microenvironment.