The scientific community believed that breast tumors released metastatic cells continuously, but a Swiss scientific team found that cancer cells that circulate and later form metastases arise mainly during the sleep phase.
This is the main finding of a study of 30 patients and mouse models published in the journal Nature, led by researchers from the École Polytechnique Fédérale (ETH) Zurich, the University Hospital Basel and the University of Basel.
Breast cancer is one of the most common forms of cancer, according to the World Health Organization (WHO). Each year, about 2.3 million people contract the disease worldwide.
If doctors detect the cancer in time, patients usually respond well to treatment. However, things become much more difficult if the cancer has already metastasized, recalls ETH.
Metastasis occurs when circulating cancer cells break away from the original tumor, travel through the body through blood vessels, and form new tumors in other organs.
According to those responsible for the work, so far cancer research has not paid much attention to this question of when tumors release metastatic cells.
This new study led to “a surprising conclusion”: the circulating cancer cells that later metastasize mainly arise during the sleep phase.
Hormones regulated by the circadian rhythm control metastasis.
“When the affected person is sleeping, the tumor wakes up”, summarizes study leader Nicola Aceto, professor of Molecular Oncology at ETH Zurich.
During the study, which involved 30 cancer patients and mice, the researchers found that the tumor generates circulating malignant cells when the body is asleep.
Cells that leave the tumor overnight also divide more rapidly and therefore have a greater potential to metastasize than cells that leave the tumor during the day.
“Our research demonstrates that the release of circulating cancer cells from the original tumor is controlled by hormones such as melatonin, which determine our daytime and nighttime rhythms,” added Zoi Diamantopoulou.
What’s more, the study indicates that the time at which tumor or blood samples are taken for diagnosis can influence oncologists’ conclusions.
According to the Swiss center, it was an accidental finding in this sense that put investigators on the right track for the first time.
Scientists were surprised to find that samples taken at different times of day had very different levels of cancer cells.
“In our opinion, these results may indicate the need for health professionals to systematically record the time at which they perform the biopsies”, says Aceto, underlining: “It can help to make the data really comparable”.
The researchers’ next step will be to find out how these findings can be incorporated into existing cancer treatments to optimize therapies.
Aceto wants to investigate whether different types of cancer behave similarly to breast cancer and whether existing therapies might be more successful if patients are treated at different times.