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Breast cancer spreads more aggressively at night

When women with metastatic breast cancer fall asleep at night, their cancer wakes up and begins to spread. This is the surprising finding of a study published in Nature. By disrupting the sleep cycle in the mice, the team also reduced the number of metastatic cells.

Nicola Aceto and his team at ETH Zurich began working on the topic after pointing out an unexplained difference in the number of circulating tumor cells in samples analyzed at different time points. of the day. Studies in mice have also shown something unusual. Indeed, there are always a higher number of cancer cells found in mice than in humans. However, we know that scientists generally take the samples when the mice are at rest.

To learn more about this cancer and circadian rhythm relationship, the researchers recruited thirty women suffering from breast cancer. Of this sample, 21 patients had early-stage cancer and nine had stage IV metastatic disease . After analysis of their blood, it was found that most of the circulating tumor cells (more than 78%) were found in blood samples taken at night .

The researchers also obtained similar results after injecting mice with breast cancer cells and then collecting blood samples during the day. Again, circulating tumor cells were significantly higher when the mouse was at rest .

Many more metastases at night

Another surprising point:cancer cells collected overnight were much more likely to metastasize . Conversely, circulating tumor cells generated during the active phase lacked metastatic capacity.

In experiments, the researchers then disrupted the circadian rhythm of some mice by changing the light-dark routine. This would then have resulted in a massive decrease in the concentration of circulating tumor cells. Giving hormones similar to those found in the bodies of mice when they are awake (testosterone, insulin and dexamethasone) would also have lowered the number of tumor cells circulating when the mouse was at rest. This research shows that the spread of cancer cells circulating from the original tumor thus seems to be hormonally controlled .

Recall that breast cancer is one of the most common forms of cancer. There are approximately 2.3 million cases worldwide each year. Patients generally respond well to treatment if the disease is detected early enough. However, treatment may be more difficult in case of metastasis .

There is still work to do. Scientists will now try to figure out how the findings can be incorporated into existing cancer treatments. These new findings, however, suggest that when blood or tumor samples are taken may alter the results. It will therefore be very important to take this factor into account in the future in the monitoring of the disease.