Breast cancer spreads most while patients sleep, new research suggests.
Researchers say the finding could significantly change the way cancer is diagnosed and treated in the future.
They add that their study may also suggest that doctors need to note when cancer biopsies are performed, as it can also affect the number of cancer cells detected.
According to the World Health Organization (WHO), breast cancer is one of the most common types of cancer and affects around 2.3 million people worldwide every year.
When the affected person sleeps, the tumor awakens
Nicola Aceto, ETH Zurich
When the disease is caught early enough, patients usually respond well to treatment, researchers say.
However, it becomes more difficult when the cancer has already metastasized – spread to other parts of the body.
Metastases occur when circulating cancer cells detach from the original tumor, travel through blood vessels throughout the body, and form new tumors in other organs.
The new study by researchers from ETH Zurich, the University Hospital Basel and the University of Basel found that circulating cancer cells, which later form metastases, mainly arise during sleep.
Study leader Nicola Aceto, Professor of Molecular Oncology at ETH Zurich, Switzerland, said: “When the affected person is asleep, the tumor wakes up.”
“Our research shows that the escape of circulating cancer cells from the original tumor is controlled by hormones such as melatonin, which determine our day and night rhythm,” adds Zoi Diamantopoulou, first author of the study and postdoc at ETH Zurich.
We believe these findings may indicate that healthcare professionals systematically record the time they perform biopsies
Nicola Aceto, ETH Zurich
The study involved 30 female cancer patients and mouse models, and the researchers found that the tumor generated more circulating cells during sleep.
According to the researchers, cells that leave the tumor at night also divide faster and therefore have a higher potential to form metastases than circulating cells that leave the tumor during the day.
The scientists were also surprised that samples taken at different times of the day showed vastly different amounts of circulating cancer cells.
Another clue was the high number of cancer cells per unit of blood in mice compared to humans.
As nocturnal animals, mice sleep during the day while scientists collect most of their samples.
Prof Aceto said: “In our view, these results may indicate that healthcare professionals need to systematically record the time at which they take biopsies.
“It can help make the data really comparable.”
Next, the researchers hope to figure out how these findings can be integrated into existing cancer treatments to optimize therapies.
The results are published in the journal Nature.