Tumor dormancy of primary and secondary cancers

Tumor doramncy is a phenomenon whereby cancer cells persist below the threshold of diagnostic detection for months to decades. This condition may arise due to either cell cycle arrrest or a dynamic equilibrium state in which cell proliferation is in balancef with cells undergoing apoptosis. Tumor dormancy isusually a reference to occult cancer cells that persist for an extended perios of time after treatment, but primary cancers can also exhibit extended growth plateaus below the limits of detection, For example, autopsies of individuals who died of trauma reveal that most individuals harbor microscopic primary cancers. Mechanisms that operate independently or succesively may restrict tumor expansion throughout tumor progression from incipiency to late-stage cancer. Proposed mechanisms include cell cycle withdrawal, immune surveillancfe, and blockes angiogenesis. The precise mechanisms underlying dormancy remain to be established, and relevant models will have an important impact on diagnostic and therapeutic stratergies for treating cancer. This review summarizes the phenomenon of tumor dormancy, experimental models, and potential mechanisms.