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Can stress cause cancer, or even hasten a patient's death? It's a daunting, emotionally charged question with no simple answers, but it represents a growing field of research that scientists hope could eventually lead to breakthroughs in cancer treatment.

The premise driving the theory is that stress has been found to weaken the body's immune response and cause some physiological changes, such as the secretion of certain hormones, that could contribute to the development of cancer.

Traditionally, much of the study in this field has focused on the effects of stress on the immune system.

But now, attention is shifting to the relationship between stress and gene function, an area many scientists believe is the key to unravelling this mystery.

Scientists have discovered that high-stress situations can cause certain genes to become activated while others, such as those responsible for suppressing the growth of tumours, may be turned off, changes that could have serious implications in the development of cancer. But a major challenge is understanding how this complex genetic relationship works and what causes changes to occur.

This research is part of epigenetics, a promising field of science that focuses on how certain factors can cause genes to be turned on or off.

New clues in this complicated puzzle emerged this week when researchers revealed a study that showed mice living in stressful conditions developed much larger cancerous tumours than those living in relatively stable conditions.

In the study, published in the journal Cancer Prevention Research, scientists used a group of female mice predisposed to developing mammary gland cancer to study the possible role played by stress. They put some of the mice in social isolation, keeping them alone in cages shortly after they were weaned from their mothers, while other mice were caged in groups. For mice, social animals that usually live in groups of three or four in the wild, isolation can trigger a significant amount of stress.

Researchers, led by Suzanne Conzen, associate professor of medicine in the Ben May Department for Cancer Research at the University of Chicago, found that the mice kept in isolation developed more cancer and had larger tumours than the mice that lived in groups.

They also found that socially isolated mice behaved differently than mice kept in groups, becoming less exploratory, and released significantly more cortisol, often referred to as the “stress hormone” because it is secreted in response to agitation or anxiety. Cortisol can also alter the body's genetic pathways and disrupt the ability of genes that suppress tumour growth to function properly.

The study provides some of the strongest evidence to date that an individual's stress level may be linked to the progression of cancer. But the quest to understand why – and, perhaps more importantly, how those factors might be used to help prevent or treat cancer – is still in its infancy.

Part of the reason is that the scientific community has yet to reach consensus on whether an individual's mental state has a real, measurable impact on susceptibility to developing cancer or the ability to fight it off. While some research has shown that cancer patients who receive extensive therapy and support live longer than those who don't, other studies have been inconclusive or shown no difference. in outcomes between patients who were anxious or unhappy and those who weren't. In fact, a study published last month in the journal Brain, Behavior, and Immunity found that short-term stress stopped the development of cancer in mice.

“This is an area that has a long way to go in terms of understanding how these factors play out in humans,” said Caryn Lerman, a professor of psychiatry and scientific director of the Abramson Cancer Center at the University of Pennsylvania.

Confounding the issue further is that people respond to stress in different ways and have varying thresholds for coping with difficult situations. As a result, the potential ability of stress to affect the development or progression of cancer may change person to person, making it that much more challenging to understand.

Instead of framing the discussion around cause and effect, one scientist who has studied this area for years said it's more accurate to think of the relationship between stress and cancer as one of potential risk.

“Stress doesn't give you cancer, but it is a risk factor like genetic differences, like environmental carcinogens,” said David Spiegel, associate chair of the Department of Psychiatry and Behavioral Sciences at Stanford University School of Medicine. “There are a whole bunch of risk factors. Not everybody that smokes tobacco gets lung cancer.”