When breast cancer patients sleep, tumor cells may “awaken” and spread through the bloodstream, a surprising study out of Switzerland reveals.

Circulating cancer cells that later form new growths (metastases) do not arise continuously as previously assumed, according to researchers at ETH Zurich, the University Hospital Basel and the University of Basel.

“When the affected person is asleep, the tumor awakens,” said study leader Nicola Aceto, a professor of molecular oncology at ETH Zurich.

Lead study author Zoi Diamantopoulou, a postdoctoral researcher at ETH Zurich, added, “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.”

About 2.3 million people worldwide develop breast cancer each year. When their cancers are detected early, patients usually respond well to treatment, the authors noted. But treatment is more difficult if a cancer spreads, which occurs when cells break away from the original tumor and travel through the blood vessels to other spots in the body.

The new study included 30 breast cancer patients and mouse models.

The researchers discovered that tumors generate more circulating cells when the host is asleep.

Cells that leave the tumor at night also divide more quickly and thus have a higher potential to form new tumors than circulating cells that leave the original tumor during the day.

As such, the time of day when tumor or blood samples are collected for diagnosis may also influence findings. This was discovered by accident when colleagues worked unusual hours, Aceto said in an ETH Zurich news release.

Another clue about the impact of sleep was the surprisingly high number of cancer cells found per unit of blood in mice compared to humans, the researchers noted. As nocturnal animals, mice sleep during the day, which is when scientists collect most of their samples.

“In our view, these findings may indicate the need for health care professionals to systematically record the time at which they perform biopsies,” Aceto said. “It may help to make the data truly comparable.”

The researchers next need to figure out how these findings can be used to get the most from existing cancer treatments.

Aceto also wants to investigate whether different cancers behave like breast cancer and whether existing therapies can be made more successful if patients are treated at different times.

The findings were published June 22 in Nature.

More information

The American Cancer Society has more on breast cancer.

SOURCE: ETH Zurich, news release, June 22, 2022

Source: HealthDay