Scientists’ unusual working hours lead to surprising discovery: breast cancer usually spreads overnight

When the person sleeps, the tumor awakens.

Scientists sometimes work at impossible times. Some can be found in the lab at dawn, while others are there late at night. These shifting working hours have now led to a remarkable discovery about when cancer cells spread. And that could significantly change the way cancer is diagnosed and treated in the future.

breast cancer

Breast cancer is one of the most common forms of cancer, according to the WHO. Each year, approximately 2.3 million people worldwide contract this debilitating disease. When doctors detect breast cancer early, patients usually respond well to treatment. However, it becomes much more difficult once the cancer has already spread. Metastases of malignant tumors occur when cancer cells separate from the original tumor and then travel through the body via blood vessels. This can result in tumors colonizing other organs as well.

Time of day

To date, no real research has been done into exactly when tumors reject metastatic cancer cells. Researchers actually assumed that tumors continuously release such cells. But a new study, published in Nature, makes a surprising discovery: circulating cancer cells that later form metastases, mainly during a person’s sleep phase, detach from the original tumor. “When the person sleeps, the tumor wakes up,” said study researcher Nicola Aceto.

Study

The study involved 30 female cancer patients as well as mice. Next, the researchers found that tumors in both generate more circulating cells during sleep. Cells that leave the tumor at night also divide faster and therefore have a greater chance – compared to circulating cells that the tumor rejects during the day – to form metastases elsewhere in the body. But why? “Our findings show that hormones such as melatonin – which determines our day and night rhythm – control the rejection of circulating cancer cells,” said researcher Zoi Diamantopoulou.

Unusual working hours

The researchers actually came across this discovery by accident. As mentioned, scientists sometimes have slightly different working hours. “And sometimes we also analyze blood at unusual hours,” Aceto says. The scientists were surprised to find that samples taken at different times of the day contained very different levels of circulating cancer cells. In addition, they found a much higher number of cancer cells per unit of blood in mice than in humans. The reason was that mice, being nocturnal animals, sleep during the day. And that’s exactly when the researchers collected the most samples.

According to Aceto, it would be good if doctors from now on systematically register the time at which they take samples. “This can help compare data better,” he says. In addition, the researchers plan to determine in follow-up research how the findings from the study can be incorporated into existing cancer treatments, with the aim of optimizing them. For example, Aceto wants to study whether interventions are more successful if the patient is treated at specific times. In addition, the research team wants to determine whether other forms of cancer also generate cancer cells that spread at night.