It Grows at Night

Scientists studying relationships between 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, circadian-aligned strategies for treating cancer.

Researchers at Israel's Weizmann Institute of Science have found evidence that suggests 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 between 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 receptor, EGFR (epidermal growth factor receptor), assists in cell growth and division. EGFR is involved in normal cell growth, and also in the growth of cancer cells. 

High levels of EGFR are found in many cancer cells, and one type of current cancer treatment works to fight cancer by inhibiting EGFR levels.

The second receptor involves a type of steroid hormone known as glutocorticoids (GC). 

Glutocorticoids perform a number of essential functions, one of which is a role in supporting daytime energy and alertness. 

When the body is under stress, levels of glutocorticoids rise sharply, heightening and sharpening a sense of alertness. Cortisol, often referred to as the "stress hormone," is one important glutocorticoid.

Glutocorticoid 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 plummet to their lowest levels at night during sleep, before rising again as morning arrives.

Scientists investigated how the circadian changes in GC hormone levels might affect the activity of EFGR, the receptor involved in cell growth. Using mice, they discovered that EGFR is significantly more active at night (when GC levels are low), and less active during the day (when GC levels are high).