New Study Reveals How Breast Cancer Impacts Sleep, Stress, and Brain Function

Cancer is usually thought of as a disease of rogue cells, growing where they shouldn’t. But emerging science suggests its reach is far wider, far sneakier. Long before a lump is felt or a scan lights up, cancer may already be disturbing the brain, throwing its internal timing out if sync. Researchers at Cold Spring Harbor Laboratory have uncovered evidence that breast cancer can disturb the brain’s natural day–night rhythm almost immediately. The result is a plethora of effects that help explain why so many people with cancer struggle with anxiety, broken sleep and exhaustion, even in the earliest stages. The study focuses on the brain’s stress system, a finely tuned feedback loop linking the hypothalamus, pituitary gland and adrenal glands. Together, they regulate the rise and fall of stress hormones, cortisol in humans, across the day. Also read | Senior oncologist reveals 8 breast cancer symptoms many women ignore until it’s too late Under healthy conditions, these hormones peak and dip like clockwork, helping us wake, rest, recover and fight infection. However, in mice with breast cancer, that rhythm collapsed. Instead of rising in the morning and falling at night, stress hormone levels became eerily flat. This loss of rhythm was linked to poorer wellbeing and shorter survival. Crucially, the disruption appeared early, within days of cancer developing, before tumours could even be physically detected. Anxiety and insomnia often arrive early Disrupted biological rhythms are already known to fuel anxiety, low mood and insomnia. When the brain no longer knows when to switch stress on or off, the body stays stuck in a state of quiet alarm. According to assistant professor Jeremy Borniger, the brain is exquisitely sensitive to imbalance. Even a small shift in timing can change how the entire system behaves. What surprised the researchers most was how quickly cancer interfered with this balance. The brain seemed to sense something was wrong in the body and responded, just not in a helpful way. Also read | How you can improve life after an early breast cancer diagnosis: from treatment plans to lifestyle habits Resetting the clock shrank tumours When scientists looked closer at the hypothalamus, they found certain neurons locked into constant activity, firing weak signals instead of following a healthy day–night pattern. By gently stimulating these neurons to mirror a normal rhythm, stress hormone cycles snapped back into place. Immune cells flooded into the tumours. And the tumours themselves shrank, without a single anti-cancer drug. Timing, however, was everything. The same stimulation applied at the wrong time of day had no effect, underlining how critical the brain’s internal clock really is. The future cancer care Cancer may disrupt the brain before symptoms appear Anxiety and sleep problems could be biological, not just emotional Restoring healthy rhythms might boost immunity Future treatments could focus on strengthening the body, not just attacking tumours The hope is that by supporting the brain and body’s natural balance, existing cancer treatments could work better, with fewer side effects. Sometimes, it seems, helping the body remember the time of day may be a powerful form of medicine in itself.