Circadian rhythm disruption contributes to the development of aggressive breast cancer

Working night shifts, frequent jet lag and erratic sleep patterns are not only taxing on the body, but are also associated with an increased risk of developing particularly aggressive breast cancer. For a long time, scientists did not understand why this happens. New research from the College of Arts and Sciences at Texas A&M University sheds light on this connection. Scientists have shown that disruptions in circadian rhythms change the structure of breast tissue and weaken immune defenses, and have also identified a possible way to counteract these effects.

Circadian rhythms are the body’s internal clock that operates on a 24-hour cycle. They regulate not only sleep, but also the production of hormones, recovery processes and immune function. To study the impact of disruptions to these rhythms, the researchers observed two groups of genetically modified animals prone to developing aggressive breast cancer. One group lived under a normal alternation of day and night, the other – under constantly changing lighting, which knocked down the biological clock.

The results, published in the journal Oncogene, were impressive. Typically, tumors appear around the 22nd week, but in animals with disrupted rhythms, cancer appeared as early as around the 18th week. Moreover, their tumors grew faster and more often metastasized to the lungs – an important sign of a poor prognosis. The disruption of the internal clock also weakened the immune system, creating a more favorable environment for tumor cells. The changes also affected healthy breast tissue – it became more susceptible to cancer.

While studying the mechanisms, scientists turned their attention to the molecule LILRB4, a receptor known for its role in suppressing the immune response. Under normal conditions, it protects tissues from excessive inflammation, but in cancer it turns into a factor that turns off the immune defense.

When the researchers blocked this “control switch,” the immune system was again able to fight off the disease more effectively. This opens up the prospect of new treatments for aggressive forms of breast cancer associated with disruption of circadian rhythms.

Thus, the work experimentally confirms that constant disruptions in the internal biological clock do not just coincide with an increased risk of cancer – they can enhance its progression. And at the same time it shows that intervening in these mechanisms can help reduce the harm caused by chronic violations of the regime.