Sleep is critical for good health. Studies show that people who don’t get good quality sleep may be at risk for many diseases and disorders, from heart disease and stroke to obesity and dementia. In addition to offering preventative benefits, sleep is often touted as a miracle cure, helping the body recover from illness and surgery. The research suggests that most cells in our body work harder when we're awake.
However, a recent study from Switzerland found that breast cancer cells may be the exception, spreading faster while the body and mind rest.
The acceleration of cancer cells affects how breast cancer metastisizes. Metastases occur when circulating cancer cells break away from the original tumor, travel through the body via blood vessels, and form new tumors in other organs. Cancer is more challenging to treat once it metastasizes. Before this study, researchers thought tumors released circulating cells all the time.
Sleep Is Not the Enemy
As startling as this news is, researchers emphasize that more studies are needed to investigate the findings. Until further information is available, sleep should not be thought of as the enemy of people with breast cancer. The results have not proven that breast cancer patients don’t need sleep or should get less sleep. On the contrary, not getting enough sleep can be detrimental to people with cancer, and some studies have shown that less than seven hours of sleep per night may be linked to a higher risk of death.
Disrupting the Body’s Circadian Rhythms
The study, which included 30 female cancer patients and mouse models, confirmed that the tumor generates more circulating cells when the organism (the cells) is asleep. In addition, cells that leave the tumor at night divide more quickly and possibly have a higher potential to form metastases than circulating cells during the day.
The study tested blood collected at 4 AM and again at 10 AM from 30 women hospitalized with breast cancer. Physicians measure circulating tumor cell (CTC) levels in the blood — a type of liquid biopsy. The researchers found that the bulk of the CTCs they detected in the blood samples — almost 80% — appeared in the portion collected at 4 AM when the patients were still resting.
The study suggests cancer cells may spread more efficiently at night due to disrupting the body’s circadian rhythms and the hormones this cycle regulates. For example, the research shows that melatonin — a hormone produced by the pineal gland that dictates sleep patterns — enables the cancer cells to spread more efficiently when the body is at rest.
A person’s circadian clock is controlled by various genes that express specific molecules on a 24-hour timetable, influencing many processes in the body, including metabolism and sleep. Previously researchers believed that rogue, mutated cancer cells wouldn’t conform to a schedule.
However, disrupted circadian rhythms were listed as a “probable” carcinogen after long-term studies concluded that people who work odd hours — such as flight attendants and night nurses — were at a higher risk of developing breast cancer.
Implications for Breast Cancer Treatment
Researchers are determining how these findings can be incorporated into existing cancer treatments. For example, can existing therapies be more successful if patients are treated at different times? In addition, results could differ depending on the time doctors take tumor or blood samples.
Another theory may change timing of certain drug-targeted therapies to block cancer spread, if given during sleep when the body’s immune system has its highest activity.
In a pilot study including women with metastatic breast cancer who were given docetaxel (Taxotere) during sleep, about one-third responded well after two days compared to five days in those who received it while awake. The findings suggest sleep could give new drugs more time to work, specifically blocking or slowing down tumor growth and spread throughout the body — particularly if combined with other treatments like chemotherapy or hormone therapy.
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