Rethinking the metastatic cascade as a therapeutic target.

Metastasis is the leading cause of cancer death. The metastatic cascade is a complex yet inefficient process that we have only begun to understand in recent years. Several of the early steps of this cascade are not readily targetable in the clinic. Past therapeutic developmental strategies have not distinguished between micrometastases and overt metastases. This lack of understanding is apparent in therapies that have been developed for patients with metastatic disease that are not efficacious in patients with micrometastatic disease; that is, in the adjuvant setting. Moreover, drugs that target distant metastases often do not work in the adjuvant setting. This Review will discuss our current understanding of the metastatic cascade as it relates to therapy, emerging therapeutic targets in the metastatic process, and how novel antimetastatic therapies might be developed for clinical use.