Breast cancer is one of the most common types of cancer.

In the United States, there were about 266,120 new cases last year, according to the National Cancer Institute.

Although breast cancer is also one of the most treatable types of cancer, once it metastasizes — that is, grows and spreads — it can be quick to diversify.

When cancer tumors are so diverse, doctors may find it hard to apply the right kind of treatment, as the therapy that works for one type of tumormay have no effect on another.

Previous research that Medical News Today covered suggests that exposure to chronic (long-term) stress is one factor that contributes to cancer cell growth in breast cancer.

Now, a new study conducted by a team from the University of Basel and the University Hospital of Basel in Switzerland has uncovered further evidence to suggest that stress can fuel the spread of breast cancer tumors, perhaps also supporting their diversification.

The study — which the team carried out in a mouse model — found that stress hormones support breast cancer metastasis. The scientists also state that the stress hormone derivatives present in certain anti-inflammatory treatments could actually "disarm" chemotherapy agents.

Lead author Prof. Mohamed Bentires-Alj and colleagues explain their findings in a new study paper that appears in the journal Nature.

"Intra-patient tumor heterogeneity is an obstacle to treatment," they note, "as it causes divergence in diagnostic markers between primary tumors and matched metastases that may lead to inadequate treatment." They say that new research needs to find a way to address this mismatch.

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