The disease awakens and begins to spread when people with metastatic breast cancer close their eyes at night.
That is the startling conclusion of a report that was published in Nature this week, debunking the notion that breast cancer metastasis occurs at a constant pace all the time.
Understanding and eradicating metastasis have long been part of the hope of treating cancer. A tumor is able to do this by sending cells to the blood arteries, where they move, colonize other organs, and develop into new tumors. This mechanism accounts for nine out of 10 cancer-related deaths.
This spreading across the body is more aggressive at night, according to a recent study, which is an unexpected finding that could have significant effects on the disease's detection and care.
The Swiss researchers examined 30 breast cancer patients to see what was happening (21 patients with early breast cancer that had not metastasized and nine patients with stage IV metastatic disease).
They discovered "a striking and surprising pattern": The majority of circulating tumor cells (78.3%) were discovered in blood samples collected at night compared to a substantially lower percentage in samples collected during the day.
A similar outcome was discovered when the researchers gave mice injections of breast cancer cells and collected blood samples throughout the day. When the animal was at rest, there were significantly more circulating tumor cells.
Fascinatingly, the researchers found that the cancer cells they had gathered during the resting phase were "extremely prone to spread, whereas circulating tumor cells formed during the active phase are devoid of metastatic ability."
Cancer cells collected from mice and people at rest that have undergone genetic analysis had their expression of mitotic genes increased. They are better able to metastasize as a result, as mitotic genes regulate cell division.
By altering the mice's schedule for light and dark, the researchers conducted studies in which some mice experienced jet lag. The amount of circulating tumor cells in mice was significantly reduced when the circadian rhythm was tampered with.
In another experiment, the researchers looked at whether hormones similar to those produced by mice's bodies when they are awake would have an impact on the quantity of circulating tumor cells in dormant mice.
They administered dexamethasone (a synthetic chemical that acts like cortisol, the stress hormone), testosterone, and insulin (a hormone that enables the conversion of sugar into energy) to mice.
In a blood sample drawn during the rest period, the researchers discovered a "marked reduction" in the amount of circulating tumor cells (when the tumor would normally be most aggressive).
"Our research shows that the escape of circulating cancer cells from the original tumor is controlled by hormones such as melatonin, which determine our rhythms of day and night," Zoi Diamantopoulou, the study's first author and a molecular oncology researcher at ETH Zurich, said.
