Women with breast cancer who take beta blockers may have better odds of surviving the disease, according to two preliminary studies.
In one study, women on beta-blockers had longer progression-free survival than those not on the medication. In the other, they were less likely to be diagnosed with aggressive breast cancer or die from it.
Still, the researchers say no one should consider taking beta-blockers to stave off cancer at this point.
"We saw an association, now it's time to prove whether they are the cause," said Dr Amal Melhem-Bertrandt, who worked on one of the studies. "It's very promising, it's encouraging, but we still have to do the studies."
Beta-blockers curb the effect of stress hormones like adrenaline and noradrenaline. Cancer researchers began to take an interest in them after animal studies showed stress responses are linked to tumour growth.
"There is a lot of literature suggesting chronic stress may influence breast cancer recurrence," Dr Melhem-Bertrandt said. "We wanted to see whether blocking one of the arms of your stress response would help reduce breast cancer."
So she and her colleagues looked at medical records for some 1,400 women treated for breast cancer with chemotherapy and surgery at the M.D. Anderson Cancer Centre in Houston. About 7% of the women also happened to be taking beta-blockers.
Pathologists who examined the tumours after surgery found no differences between those from women who were on beta-blockers, mainly metoprolol and atenolol, and those who weren't.
However, the women on beta-blockers did seem to fare better afterward. At three years, 87% were alive and cancer-free, compared to 77% of those not taking the drugs.
Results were better with beta-blockers even after the researchers accounted for differences in age, cancer stage, diabetes and other factors that might influence tumour growth.
And the findings were even more striking for women with triple-negative breast cancer, which doesn't respond to hormone therapy.
"We used to think of these drugs as innocent bystanders, but it looks like they may have an effect on cancer itself," said Dr Melhem-Bertrandt.
Still, hidden factors could be at play, such as lifestyle or medication differences between the women. What's more, the study wasn't large enough to show a potential effect on overall survival.
In recent work from the UK, researchers found similar survival rates among breast cancer patients taking beta-blockers and those taking other blood pressure medications.
"Larger studies are needed to clarify the effect of beta-blockers on breast cancer outcomes," said Dr Sunil Shah, who worked on the UK study.
"But, if these benefits are confirmed, these findings are potentially important for a sub-group of women with breast cancer as beta-blockers are a relatively safe and inexpensive therapy," added Dr, Shah, of St George's University of London.
The other new study, published along with Dr Melhem-Bertrandt's results in the Journal of Clinical Oncology, tapped into data from a cancer registry and a pharmacy database in Ireland.
Women with breast cancer who were taking propranolol were much less likely to be diagnosed with advanced breast cancer than closely matched patients not on the drugs, according to Dr Thomas Barron from Trinity Centre for Health Sciences in Dublin, Ireland and colleagues.
Women taking propranolol also fared better after being diagnosed with the disease: After five years, an estimated 9% had died of breast cancer, compared to 27% of women not on propranolol.
There was no such difference for atenolol, however. That contradicts Dr Melhem-Bertrandt's findings, and suggests not all beta-blockers work the same.
With this much uncertainty, Dr Melhem-Bertrandt said, beta-blockers aren't ready for prime time yet in the breast cancer world.
"They do have side effects," she said. "They can drop your blood pressure, they can slow your heart rate. I would not recommend women go on beta-blockers as a preventive measure."
(Reuters Health, Frederik Joelving, June 2011)
A new life after breast cancer