Figure 4.

Reactivation of disseminated tumor cells in the bone marrow: Transition from dormant micrometastasis (i.e., DTCs) to micrometastasis. Incidental activation of VCAM-1, a process possibly dependent on NF-κB signaling and other unidentified mechanisms (1), in micrometastasis arrests α4b1-positive osteoclast progenitors through paracrine chemotaxis (2) and adhesion (3), this leads to a localized increase of te osteoclast progenitor population and increased mature osteoclast activity (4), activated osteoclasts resorb the bone and instigate the vicious cycle of bone metastasis (5). DTCs: Disseminated tumor cells. Adapted from Lu et al[22].