Latest discovery: When you fall asleep, cancer wakes up...

Breast cancer is one of the most common cancers, with about 2.3 million people worldwide developing the disease each year, according to the World Health Organization (WHO). If doctors detect breast cancer early, patients usually respond well to treatment. However, things can get bad if the cancer has already metastasized — when circulating cancer cells break away from the original tumor, travel through the body via blood vessels and form new tumors in other organs.

Until now, cancer research has not paid much attention to the question of when tumors shed metastatic cells. Researchers have previously assumed that tumors continuously release such cells. However, a new study by researchers at ETH Zurich, University Hospital Basel and the University of Basel has come to a surprising conclusion: circulating cancer cells that later form metastases appear mainly during the sleep phase of affected individuals. The results of the study have just been published in the journal Nature.

"When the affected person is asleep, the tumor wakes up," summarizes Nicola Esto, professor of molecular oncology at ETH Zurich and head of the study. In their study, which included 30 female cancer patients and mouse models, the researchers found that tumors produce more circulating cells when the organism is asleep. Compared with circulating cells that leave the tumor during the day, cells that leave the tumor at night divide faster and are therefore more likely to form metastases.

"The escape of circulating cancer cells from the original tumor is controlled, among other things, by melatonin, a hormone that determines our circadian rhythm," said Zoe Diamantoplou, a postdoctoral researcher at ETH Zurich and the study's lead author.

The study also suggests that the time of day when tumor or blood samples are collected for diagnosis may affect what oncologists find. The researchers were surprised to find very different levels of circulating cancer cells in samples collected at different times of the day. A surprisingly large number of cancer cells were found per unit of blood in mice compared to humans. The reason is that as nocturnal animals, mice sleep during the day, which is when scientists collect most of their samples.

Next, the researchers will work out how to incorporate these findings into and optimize existing cancer therapies, and investigate whether different types of cancer behave similarly to breast cancer and whether existing therapies would be more successful if patients were treated at different times.

Source: Science and Technology Daily

◎ Science and Technology Daily reporter Zhang Mengran

Editor: Wang Chengyue

Review: Yue Liang

Final judge: Wang Tingting