By Andrea Hargraves 
This is the main finding of a study of 30 patients and a mouse model published in Nature, led by researchers from the Ecole Polytechnique Fédérale (ETH) in Zurich, University Hospital Basel and University of Basel.
Breast cancer is among the most common types of cancer, according to the World Health Organization (WHO). Each year, about 2.3 million people fall ill with the disease worldwide.
If doctors detect cancer in time, patients usually respond well to treatment. However, things get more difficult if the cancer has already spread, ETH recalls.
Metastasis occurs when metastasized cancer cells separate from the original tumor and travel through the body through blood vessels, forming new tumors in other organs.
According to those responsible for this work, cancer research has so far not paid much attention to the question of when tumors release metastatic cells.
This new study led to a “surprising result”: metastatic, metastatic cancer cells arise mainly during the sleep phase.
Hormones regulated by the circadian rhythm to control metastasis.
“When the affected person sleeps, the tumor wakes up,” summarizes study leader Nicola Assetto, professor of molecular oncology at ETH Zurich.
During the study, which included 30 cancer patients and mice, researchers found that the tumor generates metastatic malignant cells when the body is asleep.
Cells that leave a tumor overnight divide more quickly, and therefore have a greater ability to metastasize than cells that leave a tumor during the day.
“Our research shows that the release of metastatic cancer cells from the original tumor is controlled by hormones such as melatonin, which determine our day and night rhythms,” added Zoe Diamantopoulou.
Furthermore, the study notes 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 discovery in this sense that put the investigators on the right track for the first time.
Scientists were surprised to discover that samples taken at different times of the day contained very different levels of cancer cells.
“In our view, these findings may indicate the need for health professionals to systematically record when they perform biopsies,” says Aseto, emphasizing, “it can help make the data truly comparable.”
The next step for researchers will be to find out how these findings can be incorporated into existing cancer treatments to improve treatments.
Aceto wants to investigate whether different types of cancer behave similarly to breast cancer and whether current treatments might be more successful if patients were treated at different times.