Working night shifts, frequent travel across multiple time zones, and irregular sleep patterns may increase the risk of developing aggressive breast cancer. This conclusion was reached by researchers from the College of Arts and Sciences at Texas A&M University. The study findings were published in the journal Oncogene.

“Circadian rhythms—the body’s internal 24-hour biological clock—regulate not only sleep, but also hormone production, tissue repair, and immune function. When these rhythms are chronically disrupted, the body’s natural anti-tumor defenses are weakened,” explained Dr. Tapasree Roy Sarkar, co-director of the Center for Statistical Bioinformatics at the Texas A&M College of Arts and Sciences.

To investigate this effect, the researchers used two groups of genetically modified mice predisposed to aggressive breast cancer. One group lived under a normal light–dark cycle, while the other was kept under conditions of constant disruption of the light cycle.

In animals with disrupted circadian rhythms, tumors appeared significantly earlier—around the 18th week instead of the usual 22nd week. In addition, these tumors were more likely to metastasize to the lungs, a factor associated with a poorer prognosis.

The analysis showed that disruption of the biological clock suppressed immune defenses while simultaneously altering the structure of healthy breast tissue, increasing the risk of malignant transformation.

A key factor identified was the LILRB4 receptor—an immune checkpoint that normally limits inflammation but, in cancer, can excessively suppress the immune response. Targeting LILRB4 made the tumor microenvironment less immunosuppressive, and slowed tumor growth and metastasis even in the presence of disrupted circadian rhythms.

The authors noted that a significant proportion of the world’s population works night shifts. Their next major project will focus on exploring ways to reverse the effects of chronic circadian rhythm disruption in humans.