Circadian disruption and cancer risk: a new concept of stromal niche (review).

Circadian rhythms regulate a variety of physiological functions. Epidemiological evidence indicates that disruption of these circadian rhythms might be linked to cancer. In general, imbalances in homeostasis, such as immune and hormonal dysfunctions, are thought to be involved in cancer development. The results of a recent study suggested that circadian disruption may induce stromal changes associated with cancer risk, highlighting the importance of the cancer stem cell niche for protecting cancer cells. Current research provides new concepts and clarification regarding the function of the tumor niche, and the new concept of a stromal niche may help us to understand the additional functions of both cancer-associated fibroblasts and the extracellular matrix. In this review, we summarize our current knowledge regarding the role of circadian rhythms in cancer risk and the relevance of the stromal niche in cancer cell survival and progression.