Scientists studying relationships among different types of cells have encountered some new and potentially important information about how—and when—cancerous tumors grow most aggressively. According to a new study cancerous tumors may grow faster at night, during the hours typically taken up by sleep. Their discovery may point the way toward new, sleep rhythm-aligned strategies for treating cancer.
Researchers at Israel’s Weizmann Institute of Science have found evidence that some cancers may grow more quickly during nighttime, resting hours than during the waking day.
The finding came as a surprise to researchers, who originally set out to examine the relationships among cell receptors, molecules that are involved in cell-to-cell communications. In particular, researchers were investigating the relationship between two types of cell receptors. The first, EGFR (epidermal growth factor receptor), is involved in cell growth and replication and is part of both normal and cancerous growth of cells. With that said, cancer cells often make more EGFR receptors so that they’re more sensitive to growth signals. As a result, drugs that block the EGFR receptor are sometimes used to battle tumor growth.
The second player involved in timing of tumor growth is a type of steroid called glucocorticoid (GC). GCs perform a wide variety of roles, one of which is to support daytime energy and alertness. Cortisol, often referred to as the “stress hormone,” is one important GC. When the body is under stress, levels of GCs rise sharply, heightening and sharpening how awake you feel.
GC hormone levels rise and fall in alignment with a 24-hour circadian cycle. During active daytime hours, GC levels are at their highest, when we need to be alert and energized. GC levels are lowest at night during sleep, before rising again as morning arrives.
Scientists investigated how the daily changes in GC hormone levels might affect the activity of EGFR, the receptor involved in cell growth. Using mice, they discovered that EGFR is significantly more activated at night when GC levels are low and is less activated during the day when GC levels are high.
Having discovered this relationship between EGFR and GC, researchers next wanted to explore the possible effects of targeting cancer treatments using this new information. The researchers gave mice a form of cancer influenced by EGFR, a cancer drug that inhibits the receptor. They gave the drug at different times through the day and night. They found that mice treated during sleeping hours showed much smaller tumors than mice treated during waking hours.
These results suggest that the varying levels of GC over the course of 24 hours are involved in the degree of tumor growth in cancers that use the EGFR receptor for growth. The findings also show that giving certain treatments at night may be more effective than during the day in people with cancers that use EGFR.
This research has only been done once in mice and needs further testing and follow-up research to be shown to be correct. But it represents a potentially significant step forward in our understanding of how our body clock could influence cancer growth and how we might time delivery of anticancer therapies to make the most impact.
This research adds to growing evidence that disrupting our body clock, often with insufficient sleep, could increase the risk of cancer, contributing to more aggressive forms of the disease. These disruptions can lead to changes in cell behavior and DNA, opening pathways to the development of cancer.
There is also evidence that poor quality, fragmented sleep decreases the immune system’s ability to fight cancer, enabling tumor growth to become more aggressive. In that vein, research has linked moderate and severe obstructive sleep apnea, which prevents a person from getting good quality sleep, with significantly higher risks for cancer and higher rates of death in people who do have cancer.
All of this research shows how important keeping a consistent sleep schedule is and tells us why we need to make high-quality sleep a daily priority. As we’ve seen, getting a good night’s sleep may be a key way to battle back against cancer.