Circadian rhythms play role in cancer research.

Over the years, studies have established that circadian clocks, the internal timekeepers that run many biological processes on a near 24-hour schedule, are associated in some way with tumor growth. What's not known is precisely how the relationship works. But now researchers are uncovering some of the clock's key cancer-related components and beginning to envision a time when manipulating or taking advantage of these internal mechanisms could play a role in treating or even preventing cancer. " We are just learning which components of the circadian timing system are essential in [tumor development and progression] " , says We have " a long way to go to identify specifi c pathways that are controlled by the circadian clock, " says Marina Antoch, Ph.D., of the Lerner Research Institute in Cleveland, " but that is definitely the goal. " On a molecular level, the mamma-lian circadian clock consists of a handful of proteins that, because of positive and negative interactions with each other, are expressed periodically with a 24-hour rhythm. These clock proteins in turn drive the cyclical expression of several hundred other proteins that regulate processes such as hormone release, the sleep – wake cycle, and cell division. The clock can keep accurate time even in constant darkness, but it is also reset by light, so that an organism's metabolism and behavior will quickly fall into sync with local environmental light conditions. The body's master clock resides in a region of the brain known as the suprachias-matic nuclei (SCN), but cells in most tissues ex press the clock proteins and can maintain a circadian rhythm in the absence of direction from the SCN. Observational studies have shown that people and animals whose circadian rhythms are chronically disrupted, due to either environmental conditions or defects in clock components, are more likely to get cancer. In one well-known study, Eva S. Schernhammer, M.D., of Harvard Medical School in Boston and colleagues looked at the effects of night shifts on cancer risk among 85,000 participants in the Nurses' Health Study. They found that nurses who worked for many years on rotating night shifts, and consequently experienced prolonged exposure to artifi cial light at night, were 36% more likely to develop breast cancer and 35% more likely to develop colon cancer than their peers who never worked at night. Other observational studies have supported these fi ndings. In the 5 years since publication of …