When sleep falls apart, health often follows. New research shows that the effects extend beyond short-term fatigue, linking irregular sleep and light schedules to a higher risk of aggressive breast cancer.

For years, scientists noticed that night-shift workers and frequent travelers faced higher cancer rates. The reasons stayed unclear.

The latest findings help explain what happens inside the body when normal rhythms break down, and why cancer may thrive in that chaos.

How sleep affects breast tissue

The body’s daily timing system quietly runs the show. It controls sleep, hormones, tissue repair, and immune patrols that hunt for threats.

When this system stays out of sync, those protections weaken, and harmful cells can gain ground.

Circadian rhythms guide how breast tissue grows and repairs itself. When those rhythms stay stable, cells follow clear rules. When they do not, the structure of breast tissue can change in ways that leave it more open to disease.

The work came from Texas A&M University College of Arts and Sciences, led by Dr. Tapasree Roy Sarkar. Her team set out to understand how disrupted timing affects cancer growth at the tissue and immune levels.

“Cancer keeps time,” Sarkar said. “If your internal clock is disrupted, cancer takes advantage – but now we’ve found a new way to fight back.”

Inside the experiment

Researchers studied two groups of genetically engineered models that develop aggressive breast cancer. One group lived under normal day-night light cycles. The other experienced disrupted lighting that interfered with internal timing.

The difference was clear. Cancer usually appeared around 22 weeks in models with normal rhythms. In the disrupted group, cancer signs showed up much earlier, close to 18 weeks.

Tumors also behaved more aggressively and spread more often to the lungs, a warning sign linked to poor outcomes in patients.

Beyond tumor growth, immune defenses dropped. The body’s natural surveillance slowed, creating conditions that allowed cancer cells to survive and spread.

“It wasn’t just that tumors grew faster,” Sarkar said. “The immune system was actively restrained, creating more favorable conditions for cancer cells to survive and spread.”

Changes beyond the tumor

The damage did not stop at the cancer itself. Long-term disruption altered healthy breast tissue as well.

Researchers observed structural changes in mammary glands, the milk-producing tissue of the breast, that made the tissue more vulnerable to cancer over time.

“We observed clear changes in the morphology of the mammary glands, the milk-producing tissue of the breast,” Sarkar said.

These findings suggest that disrupted timing can reshape healthy tissue long before cancer fully forms, setting the stage for faster progression later.

A key immune checkpoint

A closer look inside the tumors revealed a key player. One molecule, leukocyte immunoglobulin-like receptor B4, stood out.

Known as LILRB4, it regulates immune responses and helps prevent excessive inflammation in healthy tissue.

Under disrupted circadian conditions, LILRB4 activity increased inside tumors. That increase dampened immune responses that normally slow cancer growth.

“LILRB4 acts as an immune checkpoint,” Sarkar said. “When we targeted LILRB4, the tumor microenvironment became less immunosuppressive, and even under disrupted circadian conditions, we observed less cancer spread.”

When researchers adjusted LILRB4 activity, immune function improved. Tumor growth slowed, and cancer spread dropped.

“When we began to intervene and regulate LILRB4’s activity, we observed significantly less cancer metastasis and tumor growth,” Sarkar said.

Driving cancer progression

The study adds strong evidence that disrupted sleep patterns do not just link to cancer risk but can actively drive cancer progression.

“This study shows what can happen when our internal clock is repeatedly disrupted, and how we might begin to repair the damage,” Sarkar said.

“The study reframes sleep and timing as powerful players in cancer progression and treatment.”

A common risk

Irregular schedules are common. Between 12 and 35 percent of Americans work outside regular daytime hours.

That includes night shifts, rotating schedules, flight crews, and frequent travelers.

“A significant portion of the population works night or rotating shifts,” Sarkar said. “This makes understanding the impact of circadian disruptions on cancer risk incredibly important.”

Reversing circadian disruption

The research team is now exploring whether the effects of long-term circadian disruption can be reversed in people.

The goal is to improve outcomes for those whose jobs or lifestyles regularly disrupt sleep.

“Our next goal is to better understand how we can reverse the effects of circadian disruption and help advance human health with a real-world impact,” Sarkar said.

The findings place sleep and timing at the center of cancer biology. As modern life continues to blur day and night, understanding how the body keeps time may become one of the most practical tools for protecting long-term health.

The full study was published in the journal Oncogene.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates.

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–