Rauscher admits he's still a long way from the answer. "And so it's a very complicated issue to tease out what this means, other than to say that it suggests the possibility that there may be a biologic role of stress in the development of breast tumors that warrants further research."

The researchers were only able to do the stress interview after women were diagnosed with breast cancer, so they had to assume that the level of stress faced by the patients was the same before their diagnosis than after. But Rauscher concedes that is a limitation of his study.

"Therefore it's possible - even likely - that the process of diagnosis and the process of being treated influenced what they told us about their level of stress."

Raucher, who presented his study at a meeting of the American Association for Cancer Research in Washington, says more research is needed to better understand the relationship between stress and breast cancer. For a lot of reasons, it's probably good to minimize stress in our lives. But he cautions that his research does not mean that people who have had a stressful experience are necessarily at greater risk of aggressive breast cancer.